how do I solve: -3/7(m+5)=3+2m

again I am confused by your use of parentheses

I think maybe you mean:

(-3/7)(m+5) = 3+2m simply because I doubt that you are doing quadratics as you typed it with m+5 in the denominator

-3(m+5) = 21 + 14 m
-3 m - 15 = 21 + 14 m
-17 m = 36
m = -36/17