s=(2+3t)(5t-4) find ds/dt at t= 4s/2

ds/dt = (2 +3 t) (5) + (5 t - 4 )(3)

= 10 + 15 t + 15 t - 12
= 30 t - 2
if t = 4 s / 2
ds/dt = 60 s - 2