Solve the Problem

Short Answer

Solve the problem.
- $$\text { If } f ( x ) = \frac { 1 } { 2 } x ^ { 2 } + 4 \text { and } g ( x ) = 2 x - a \text {, find a so that the graph of } f \circ g \text { crosses the } y \text {-axis at } 36$$