Answer
The speed of the shadow up the wall is $~~8.7~m/s$
Work Step by Step
As the shadow moves up the wall, $\frac{\Delta y}{\Delta x} = tan~30^{\circ}$
Then:
$\frac{v_y}{v_x} = tan~30^{\circ}$
$v_y = v_x~tan~30^{\circ}$
$v_y = (15~m/s)~tan~30^{\circ}$
$v_y = 8.7~m/s$
The speed of the shadow up the wall is $~~8.7~m/s$
