The answer would be 28.
Because m=5 and n=3 we would substitute those values in the corresponding equation. So our new equation would be 2(5) + 6(3). From here we follow the rules of PEMDS (Parentheses, Exponents, Multiplication, Division, Subtraction [or addition if present]). Now we multiply our values and then add. 2×5 is 10 and 6×3 is 18. 10+18=28, thus giving us the answer of 28.