throughput accounting & bottle neck

Dear Sir

Below im putting up a question and its answer :-

QUESTION:-
Glam Co is a hairdressing salon which provides both ‘cuts’ and ‘treatments’ to clients. All cuts and treatments at the salon are carried out by one of the salon’s three senior stylists. The salon also has two salon assistants and two junior stylists.

Every client attending the salon is seen first by a salon assistant, who washes their hair; next, by a senior stylist, who cuts or treats their hair depending on which service the client wants; then finally, a junior stylist who dries their hair. The average length of time spent with each member of staff is as follows:

_______________________Cut (Hours)________Treatment (Hours)

Assistant________________ 0.1___________________0.3

Senior stylist_____________1.0 __________________ 1.5

Junior stylist _____________0.6 __________________ 0.5

The salon is open for eight hours each day for six days per week. It is only closed for two weeks each year. Staff salaries are $40,000 each year for each senior stylist, $28,000 each year for each junior stylist and $12,000 each year for each of the assistants. The cost of cleaning products applied when washing clients’ hair is $1.50 per client. The cost of all additional products applied during a ‘treatment’ is $7.40 per client. Other salon costs (excluding labour and raw materials) amount to $106,400 each year.

Glam Co charges $60 for each cut and $110 for each treatment.

The senior stylists’ time has been correctly identified as the bottleneck activity.

The salon has calculated the cost per hour to be $42.56.

Calculate the throughput accounting ratio (TPAR) for both services (to two decimal places).

ANSWER :-
Cuts

Return per hour = (Selling price – materials)/time taken on the bottleneck = (60 – 1.50)/1 = 58.50

TPAR = Return per hour/cost per hour = 58.50/42.56 = 1.37(to 2 decimal places)

Treatments

Return per hour = (Selling price – materials)/time taken on the bottleneck = (110 – 8.90)/1.5 = 67.40

TPAR = Return per hour/cost per hour = 67.40/42.56 = 1.58(to 2 decimal places)

MY DOUBT: –

im confused as to why they have calculated the revenue only on the bottle neck resource as it is not mentioned in the question it can be done on the total hrs it takes per cur or treatment .

Looking forward to your reply

Thankyou

Best Regards

Manan