Final answer:
To solve the exponential equation 87 - x = 15, subtract 15 from both sides, then subtract 72 from both sides, and lastly, divide both sides by -1 to find that x = 72.
Step-by-step explanation:
To solve the exponential equation 87 - x = 15, we need to isolate the variable x. We can do this by subtracting 15 from both sides of the equation:
87 - x - 15 = 15 - 15
72 - x = 0
Next, we can solve for x by subtracting 72 from both sides of the equation:
72 - x - 72 = 0 - 72
-x = -72
Finally, we divide both sides of the equation by -1 to solve for x:
x = 72