You said that P = I · R · T
Divide each side by I · R : P / (I·R) = T

Negative multiply negative = Positive
Negative multiply positive = negative

Thus the answer is -4a + 16b - 12c - 12d.
We know that the slope formula is m = (y1 - y2)/(x1 - x2)
Your points are: (3, 7) and (4, -8)
In this case,
x1 = 3
x2 = 4
y1 = 7
y2 = -8
Now, just plug in the numbers:
m = (7 - -8)/(3-4)
m = 15/-1
m = -15
Your slope is -15.
A is the answer because you need to know how much he spends. If wrong sorry.
Answer:
I cant really see its up side down if you can do it again the right way then I tell you what it is but its kinda hard to see the way im seeing it