jmc

We know that $(a+b{)}^2=a^2+2ab+b^2$. Therefore, we plug in the given values to get $5^2=15+2ab$. Solving, we get that $ab=5$. We also have the sum of cubes factorization $a^3+b^3=(a+b)(a^2-ab+b^2)$. Plugging in the values given and solving, we get that $a^3+b^3=(5)(15-5)=(5)(10)=\boxed{50}$.