Hello there Math master, (I wonder if I could become one later...)

I have this several questions in which I could not find the answer..I'm stuck.

If $\displaystyle 10^m = 2$ and $\displaystyle 10^n = 3$, find the value of 10^3m-n

Now I have tried randomly and find out that m = 1/5, but I do not know the proper way how to find m and n respectively. The book said that we need to find the common factor of 10 and 2, but so far I could not find any because the number seems very weird...

There's also this another question which is nearly the same:

Given that $\displaystyle 3^x = 5$ and $\displaystyle 3^y = 7$, find the value of 3^2x-3y, giving your answer in fraction.

Thank you for your kind help.