4.2³ = 74.088. If the 4.2 is accurate, this is actually not an estimate but an exact answer. You can of course round it to 74, then it becomes an estimate.
Given that height, h(t) of a tennis ball is modeled by the equation h(t)=<span>-16t^2 + 45t + 7, the time taken for the ball to reach maximum height will found as follows:
at maximum height:
h'(t)=0
but from the equation:
h'(t)=-32t+45=0
solving for t we get
t=45/32
t=1.40625~1.4 seconds
Thus the time taken to reach maximum height is 1.4 seconds
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