The temperature was 80°F and then fell 20°F.

Equation;

(3/4)x = 2/3

Solving;

x = 8/9

she would need 8/9 of her sugar to make a full batch.

Step-by-step explanation:

Let x represent the amount of sugar that would be needed to make the whole batch.

Given that;

Pia used 2/3 of her sugar to make 3/4 of a batch of cookies.

Since 2/3 of her sugar is needed to make 3/4 of a batch of cookies, then;

(3/4)x = 2/3

Solving the equation, dividing both sides by 3/4;

(3/4)x ÷ 3/4 = 2/3 ÷ 3/4

x = 2/3 × 4/3

x = 8/9

Therefore she would need 8/9 of her sugar to make a full batch.