Step-by-step explanation:
Assuming that de + ef = df, we can create the expression:
(4x + 10) + (2x - 1) = 9x - 15
Combine like terms to get:
6x + 9 = 9x - 15
The rest is basic algebra after this point.
6x + 9 = 9x - 15
-6x +15 -6x +15
______________
24 = 3x ----> x = 8
Next, plug the x value into the df equation to find df.
df = 9(8) - 15
df = 72 - 15
df = 57
