Solution:
As, Triangle ABC and Triangle A'B'C' will be similar to each other.So,their corresponding interior angles will be equal.
So, ∠A=∠A'
∠B=∠B'
∠C=∠C'
1. 4 x -4=51-x
4x +x=51+4
5 x=55
Dividing both sides by 11
x=11
2. 6 x-1= 4 x +21
6x-4x=21+1
2x=22
Dividing both sides by 2, gives
x=11
So, when x=11,the two triangles ΔABC∼ΔA'B'C by the AA criterion.