1.
[tex]h=-16t^2+vt+c\qquad\text{original equation}\\\\h+16t^2-c=vt\qquad\text{subtract terms not containing v}\\\\v=\dfrac{h+16t^2-c}{t}\qquad\text{divide by the coefficient of v}[/tex]
2. Filling in the given numbers, we have ...
[tex]v=\dfrac{131+16(3)^2-5}{3}=90\qquad\text{ft/s}[/tex]
3. The velocity is undefined when t=0. The equation is telling you it would take infinite velocity to travel some distance in zero time. The equation is meaningless in such a situation.