Question

Suppose the temperature increases 8° to -7°F what was the starting temperature
A.15°
B -20°
C.-13°
D.-15°

Answer 1

8+7=15 but because you are adding to get -7, you will have -15 (D) for your answer.

Answer 2

If you think like they teach in Algebra
x = unknown start temperature
(unknown) temperature increases 8°
write that as x + 8 (8 more than the unknown temperature x)

to -7°F

after adding 8 (increasing by 8) we get to -7
x+8 = -7

once we have an equation, we can solve it.

add -8 to both sides
x+8 -8 = -7 -8
on the left side 8-8 is 0 . on the right side -7-8= -15

x+0 = -15
or simply
x = -15

the unknown temperature is -15