Question 15bce911

The function $h$ is defined by $h\left(x\right)=4x+28$. The graph of $y=h\left(x\right)$ in the xy-plane has an x-intercept at $\left(a,0\right)$ and a y-intercept at $\left(0,b\right)$, where $a$ and $b$ are constants. What is the value of $a+b$?