Question 971088
2x^2a[8x^(5a-4)+5x^(2a+1)]=16x^31+10x^21 

16x^7a-4  + 10x^4a+1
Add exponents when distributing
Then set the exponents equal to the appropriate coefficient of the variable, 16x^  and 10x^

7a-4=31
7a=35
a=5

4a+1=21
4a=20
a=5