Answer:
MN = 56
Step-by-step explanation:
This can only be solved if we know the relation of MN to other dimensions of the trapezoid. If we assume MN is a midline (AM=MD, BN=NC), then MN is the average of the base lengths:
MN = (AB +CD)/2
2MN = AB +CD . . . . . multiply by 2
2(12x -4) = 8x +72 . . . fill in the given values for the segment lengths
24x -8 = 8x +72 . . . . . eliminate parentheses
16x = 80 . . . . . . . . . . . add 8-8x
x = 5 . . . . . . . . . . . . . . divide by 16
MN = 12(5) -4 = 56 . . . find the length of MN using its formula
