Question

Need help solving this math

Answer 1

20x(x+1)+1=y, where you know y so plug that in, distribute that, you'll get a 2nd degree polynomial, solve for x using one of several available methods, one you most likely have had hammered into your head since 8th grade.

Answer 2

The breaks are at 41, 121, 241, 401, 601, etc.  So they are pretty far apart.

You can just take the (numbers -1)/40 and round them down.  You will get integers from 1 to 50 for levels up to 9.  The breaks occur at 1, 3, 6, 10, 15 etc.
You can just loop a counter that goes up by 2, 3, 4, etc.

Answer 3

Rearrange to   20*(lvl)^(2) + 20*lvl + (1 - exp) =0

then you can put it into the quadratic formula with a=20, b=20, c=1-exp.

then simplifying, lvl = (-5+√(5*exp+20))/10

Putting in exp=41, gives lvl=1, and exp=121 gives lvl=2, etc

Most numbers don't give a whole number ofc, so round down the answer.