Answer:
m = 1 + 2log(x)/log(y)
Explanation:
Taking logarithms, you have ...
log(x) +m·log(y) = log(y) +3log(x)
m·log(y) = log(y) +2·log(x) . . . . subtract log(x)
m = (log(y) +2·log(x))/log(y) . . . divide by the coefficient of m
m = 1 +2·log(x)/log(y) . . . . . . . simplify a bit*
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* The "simplified" form will depend on your preference. Here, I like the integer 1 brought out because most logs are irrational. The result may be very slightly more accurate if we add 1, rather than log(y)/log(y)--depending on your calculator.