2^2x+ 3(2^x) - 10 = 0
6^2x-2(6^x)-15=0
3^4^5^x =336
The first one can be solved by the substitution
u=2^x
The equation transforms to
u^2+3u-10=0
(u+5)(u-2)=0
u=-5 or u=2
2^x=-5, or 2^x=2
x=log(-5)/log(2) = complex root, or
x=log(2)/log(2) = 1
The second equation can be solved similarly.
The third equation reduces to taking logs successively, which reduces to:
x=log(log(log(336)/log(3))/log(4))/log(5)