Answer:
x = 1 9/11
Explanation:
Corresponding parts of the similar triangles are proportional.
Setup
(5x +10)/21 = 10/11 . . . . . . right sides are proportional to left sides
Solution
Multiplying by 231 gives ...
11(5x +10) = 210
55x +110 = 210 . . . . . . eliminate parentheses
55x = 100 . . . . . . . . . subtract 110
x = 100/55 = 1 9/11