Find the equation of your parabola. The vertex is at (0,32)
and it passes through (42,0)
The parabola equation is y=-8x^2/441+32
Can you continue from there?. We centered the parabola at the origin.
Space your beams accordingly. You could put the first one to the right at x=6, then x=18, then x=30.
The same to the left. Add up all your y values.