9514 1404 393
Answer:
x = 10
Step-by-step explanation:
The marked sides are proportional, so we have ...
x/8 = (x +5)/12
3x = 2(x +5) . . . . . multiply by 24 to clear fractions
3x = 2x + 10 . . . . . eliminate parentheses
x = 10 . . . . . . . . . . subtract 2x
_____
Alternate solution
We observe that the difference between the upper segment lengths is ...
(x +5) -(x) = 5
and the difference between the lower segment lengths is ...
12 -8 = 4
This means the upper segment lengths are 5/4 times as long as the lower segments. Then ...
x = (5/4)(8) = 10
