Question 522085
{{{D = L ((m/r) + (u2/25))}}} 

{{{D/L =(m/r)+(u^2/25)}}}

{{{(D/L)-(m/r)=u^2/25

{{{(Dr-Lm)/Lr=u^2/25}}}


{{{25(Dr-Lm)/Lr=u^2}}}
Take the square root

{{{5*sqrt((Dr-Lm)/Lr)=u}}}