Mathematica calculus help

So this is my first time using mathematica and I am having a small problem. I thought I had figured out the question but then looked at my friend's answer and mine was just a little off so I switched around the problem to try to get his answer.

For some reason I keep getting outputs with "Pa" when I solve the equation

Said equation:

For[i = 1, i < 51, i = i + 1, Qa = (100000 - 200 Pa/3) (1.01)^(i - 1);

sol = Solve[{Qa == 50}, {Qa}]; quant[i] = First[Qa /. sol]]

Array[quant, 50]

I am trying to solve for Qa for years 1-50

Thanks for the help!