Simplify using surds:3 divided by root2+root3-5
Your words are a bit ambiguous. I'll take a stab at it. If I get it wrong, try typing what you really meant.
3/(√2+√3-5)
since (a-b)(a+b) = a^2-b^2, that gives us
3(√2+√3+5)/((√2+√3)-5)((√2+√3)+5)
3(√2+√3+5)/((√2+√3)^2 - 25)
3(√2+√3+5)/(2√6-20)
3(√2+√3+5)(2√6+20)/(24-20)
3/2 (√2+√3+5)(√6+10)
You can expand that if you want