Solving for a variable in an expression

Question

I have got this expression $X = 20t + 0.5t^2$ and the requirement for this is to solve for t. I have tried to do this by factoring t out but was not able to do it. This is what i have done: $X = 20t + 0.5t^2\\$

$X = (0.5t +20)t $

Answer 1

Hint: this is a quadratic equation.

Answer 2

multiplying by $2$ we get $$t^2+40t-2x=0$$ using the quadratic solution formula we get $$t_{1,2}=-20\pm\sqrt{400+2x}$$