Answer
$v=\sqrt{9.17s-27.7}$ ft/s
Work Step by Step
We solve for the acceleration as follows:
$v^2=v_0^2+2a_c(s-s_0)$
$8^2=3^2+2a_c(10-4)$
$a_c=4.583$ ft/s$^2$
Next, we solve for velocity:
$v^2=v_0^2+2a_c(s-s_0)$
$v^2=3^2+2(4.583)(s-4)$
$v=\sqrt{9.17s-27.7}$ ft/s