Answer:
x=9
Explanation:
We can use similar triangles and proportions to solve. Put the side of the small triangle over the side of the large triangle
9 3x-20
---------- = -----------------
9+72 3x-20 +56
Combine like terms
9 3x-20
---------- = -----------------
81 3x+36
Using cross products
9*(3x+36) = 81*(3x-20)
Distribute
27x + 324 = 243x- 1620
Subtract 27x from each side
27x-27x +324 = 243x-27x -1620
324 = 216x -1620
Add 1620 to each side
324+1620 = 216x-1620+1620
1944 = 216x
Divide by 216
1944/216 = 216x/216
9 = x