Use the distributive property to remove the parentheses?

-5*((-3v^2)+(3)-(5x^3))

to distribute this, you that the multiplying constant of -5, and multiply it by each term within the parenthesis. So;
-5*(-3v^2)=-15v^2
-5*(3)=-15
-5*(-5x^3)=25x^3
put these all together and you get the answer of 15v²+25x³-15