Question 1007977
 

we are given {{{d=0.0052s^2 + 0.13s}}}, and {{{d=20m}}}
the equation becomes
{{{0.0052s^2 + 0.13s - 20 = 0}}} and we will use the following quadratic formula to solve it for {{{s}}},

{{{s = (-0.13 +- sqrt(0.13^2 - 4*0.0052*(-20))) / (2*0.0052)}}} 

{{{s = (-0.13 +- sqrt(0.0169 + 0.416)) /0.0104}}}


{{{s = (-0.13 +- sqrt(0.4329)) /0.0104}}}

{{{s = (-0.13 +- 0.6579513659838393) /0.0104}}}

solutions:
{{{s = (-0.13 + 0.6579513659838393) /0.0104}}}

{{{s =0.5279513659838393/0.0104}}}

{{{s =50.76455442152301}}}

{{{s =50.8}}}

or
{{{s = (-0.13 - 0.6579513659838393) /0.0104}}}

{{{s =-0.7879513659838393/0.0104}}}

{{{s =-75.76455442152300961538461}}}

{{{s =-75.8}}}...disregard negative solution

and your solution is:

{{{s= 50.8(km/h)}}}