Question 932077
{{{ 40000r= (2000)* (1-(1/((1+r)^24)))}}}
{{{ 20r=1-1/(1+r)^24)}}}
{{{ 20r(1+r)^24=(1+r)^24-1)}}}
{{{ 20r(1+r)^24-(1+r)^24+1=0)}}}
{{{(1+r)^24(20r-1)+1=0}}}
It's not due to your lack of algebra skills. 
You can't get a closed form solution for {{{r}}}.
You can look to solve it numerically, but I don't think that's what you're after. 
Repost if you need more help.