Answer
$\left\langle 4,9 \right\rangle$
Work Step by Step
Suppose $u=\left\langle a,b \right\rangle$ and $v=\left\langle c,d \right\rangle$ be two vectors, then their sum is given by
$u+v=\left\langle a,b \right\rangle+\left\langle c,d \right\rangle =\left\langle a+c,b+d \right\rangle$
Now $u=\left\langle -3,5 \right\rangle$ and $v=\left\langle 7,4\right\rangle$ therefore,
$u+v=\left\langle -3,5 \right\rangle+\left\langle 7,4 \right\rangle =\left\langle -3+7,5+4 \right\rangle=\left\langle 4,9 \right\rangle$
Hence, the sum of the vectors $u=\left\langle -3,5 \right\rangle$ and $v=\left\langle 7,4 \right\rangle$
is $u + v =\left\langle 4,9 \right\rangle$.
