Answer :
max height is the vertex
convert to vertex form (y=a(x-h)^2+k) by completeing the square
h(t)=-16(t²-4t)+80
h(t)=-16(t²-4t+4-4)+80
h(t)=-16((t-2)²-4)+80
h(t)=-16(t-2)²+64+80
h(t)=-16(t-2)²+144
vertex is (2,144)
at t=2, the height is 144
max height is 144ft
convert to vertex form (y=a(x-h)^2+k) by completeing the square
h(t)=-16(t²-4t)+80
h(t)=-16(t²-4t+4-4)+80
h(t)=-16((t-2)²-4)+80
h(t)=-16(t-2)²+64+80
h(t)=-16(t-2)²+144
vertex is (2,144)
at t=2, the height is 144
max height is 144ft