Question

a body projected vertically up from ground crosses a point Pafter 4 seconds and again after 6 seconds Maximum height reached by that body above the ground is (g=10m/s)

Answer 1

due to symmetry, the max height is reached after 5 seconds.

y = vi*t - 5t^2
at t=5, v=0, so since
v = vi - 10t,
vi-10*5=0
vi=50

y = 50t-5t^2
y(5) = 50*5-5*25 = 125

Answer 2

Very badly answered the question