25^x - 9^x = 18
5^x - 3^x = 3
What's 5^x + 3^x = ?
Not as hard as it looks....!!!!
Note that 25^x - 9^x can be written as (5^x)^2 - (3^x)^2
And this will factor as a difference of squares as
( 5^x - 3^x) (5^x + 3^x)
And since this equals 18 and (5^x - 3^x) = 3
Then (5^x + 3^x) must = 6