Question 1082909
First find t when S=70.
{{{3t^2-7t+4=70}}}
{{{3t^2-7t-66=0}}}
{{{(t-6)(3t-11)=0}}}
Only positive t allowed here.
{{{t-6=0}}}
{{{t=6}}}{{{s}}}
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To find the velocity, take the derivative of S.
{{{dS/dt=6t-7}}}
So when {{{t=6}}},
{{{v=dS/dt=6(6)-7}}}
{{{v=36-7}}}
{{{v=29}}}{{{m/s}}}