Standard costing

A company’s standard labour rate for its factory workers is set at 5$ per hour.

The standard time allowed for producing one unit is 20 minutes.
During the period 4,800 units were produced and the factory workers were paid $5.25 per hour. The actual hours worked were 1,560.

What was the total labour cost variance?

solution:

1560X5.25$ = 8190
1560X5$ = 7800

my answer was 390$ (A) Adverse

but they did absolutely something different:

Aq X Ap 1560 X 5.25 = 8190
Sq X Sp 4800X20/60X5$ = 8000

the answer:190 (A)

I am never did something like this as I know we are always “comparing ” Aq X Ap vs Aq X Sp or Aq X Sp vs Sq X Sp.

But I never happen to see when it comes to figuring out variance to “compare” Aq X Ap vs Sq X Sp….

Why is that so? Can you show me a full picture of doing so ?

thanks in advance