Answer
$v_1=\frac{2s}{t}-v_2$
Work Step by Step
Multiply $2$ to both sides of the equation:
$2(s)=2 \cdot \frac{(v_1+v_2)t}{2}
\\2s= (v_1+v_2)t$
Divide $t$ to both sides of the equation:
$\frac{2s}{t} = \frac{(v_1+v_2)t}{t}
\\\frac{2s}{t}=v_1+v_2$
Subtract $v_2$ to both sides of the equation:
$\frac{2s}{t}-v_2=v_1+v_2-v_2
\\\frac{2s}{t}-v_2=v_1$