Nice i love precal here how it works
25 can be rewritten as 5^2
[(5^2)a+3]x(5^3a)
Now the base is the same you can add the exponents together! Remember You add exponents when combining them :) So
2a+6+3a
5a+6. Now You solve for a
5a+6=0
5a= -6
a= -6/5
Goodluck! :)