Question 888130
trial and error to achieve your answer:

(0.04)^-28 = 1.3877787807814456755295395851135e+39 or 1.4x10^39

having known that keep punching numbers in till you get the same answer which is 5^56 and in the question as stated is 5^2a divide 56 by 2 and your value of a is 23