MARGINAL COSTING

There is this queston confusing me as to why the variable manufacturing costs per unit was multiplied by units sold during the year instead of production units

QUESTION:

Budgeted production 80,000 units
Actual production 70,000 units
Units sold during the year 50,000 units
Selling price per unit 200

Costs
Variable costs : 8,400,000
(Of this 60% is manufacturing and 40% is selling and distribution expenses)

Fixed costs 2,020,000
(Of this 50% is manufacturing and 50% is selling and distribution expenses)

As it was the first year of operation, there is no inventory at the beginning of the year. Actual input prices per unit and actual quantities per unit of the product were equal to the standard.

SUGGESTED SOLUTION

Sales (50,000 units x Tshs200,000) 10,000,000
Less: Variable costs
Manufacturing expenses (W1) 3,600,000
Variable selling and distribution expenses (8,400 million x 0.40) 3,360,000 (6,960,000)
Contribution margin 3,040,000

Less: Fixed manufacturing cost 1,010,000
Fixed selling and distribution expenses (Tshs2,020,million x 0.50)1,010,000 (2,020,000)
Operating income 1,020,000

…………………………………………………………

What is really confusing me i that the Variable manufacturing expenses where by the variable manufacturing costs per unit (72,000 per unit) was multiplied by units sold during the year instead of production units, It was worked out as following:

Variable manufacturing costs per unit = (Tshs8,400 million x 0.60)/70,000 units
=Tshs72,000 per unit, For 50,000 units sold during year manufacturing cost is 50,000 x Tshs72,000 = Tshs3,600 million

I seek explanation on why the variable manufacturing costs per unit (72,000 per unit) was multiplied by units sold during the year instead of production units