ANSWER
When
is written in the form
, it looks like 
EXPLANATION
To write
in the form
, we have to complete the squares.
We add and subtract half the coefficient of
square.

The first three terms of the function is now a perfect square.

We now simplify rto obtain,

For 8 batches of brownies, you’ll need 4 cups of sugar
8/ Sine 50 = n/ Sine 90
8 sine 90 = n Sine 50
8 sine 90 / sine 50 = n
n = 10.4
I think it's 20. Sorry if it's wrong
The answer is 6. Hopefully this helped!!