Kaplan mtq question

Bogh Co manufactures wooden picture frames.
The company’s information system produces an operating statement, and on the basis of the
variances calculated, managers are assessed and bonuses paid.
The standard material cost for each picture frame is $8. This is made up:

Wood 0.5 kg @ $10 per kg $5
Glass 0.25 kg @ $12 per kg $3

In July, Bogh manufactured 300 picture frames, and purchased:
Wood 170 kg $2,040
Glass 70 kg $860

Required:
(a) Using the information above, calculate (to the nearest whole number):

The total materials usage variance and state if it is adverse or favourable:

I normally calculate material usage variance by using this following formula:

Actual units*standard usage XXXX
-Actual usage (XXXX)
Variance in kg -X/X
standard cost per kg $X
Variance in $ (Standard cost per kg*Variance in kg

By applying this formula, I get an answer different from that which is given in the kaplan kit:

Wood
Glass
Aq × Ap = 170 × 12
Aq × Ap = 70 × 12.29
= 2,040
= 860 = 2,900
(i) Price = $360A
Wood
Glass
Aq × Sp = 170 × 10
Aq × Sq = 70 × 12
= 1,700
= 840 = 2,540
(ii) Usage = $140A
Wood
Glass
Sq × Sp = 300 × 0.5 × 10
Sq × Sp = 300 × 0.25 × 12
= 1,500
= 900 = 2,400

Is it not possible to identify the cost per kg and get the same answer?