hint; max ht is when velocity=0.A small marshmallow is launched straight up in the air with a slingshot. Its height h in meters, relative to te ground, is given by the function h(t) = 5 + 20 - 5t^2, where t is measured in seconds. About when does the marshmallow reach its maximum height?
and as said previous you are missing a t.
h(t) = 5 + 20t - 5t^2