Question 171386
You want to find the value of t when h(t)=9


So set the expression for h(t) equal to 9 and solve for t.


{{{1+13t-5t^2=9}}}


Put it in standard form:


{{{-5t^2+13t-8=0}}}


Factors to {{{(x-1)(-5x+8)=0}}}, so {{{t=1}}} or {{{t=8/5}}}.  But the question asks for when the ball will FIRST be at 9 meters, so pick the lowest time value, namely {{{t=1}}}