Question 5

If the cross product of the vectors $\mathbf{u} = 7\mathbf{i} - 4\mathbf{j} + 5\mathbf{k}$ and $\mathbf{v} = a\mathbf{i} - b\mathbf{j} + 3\mathbf{k}$ is zero, then find the values of $a$ and $b$.