Question

I was looking at the solution steps to a problem on this website: http://tutorial.math.lamar.edu/Problems/CalcI/ExpLogEqns.aspx

the question is: log(w) + log(w-21) = 2

but in the solution steps it goes from:
10^(log(w^2-21w)) = 10^2
to:
w^2-21 = 100

My question is, where did the w in 21w go? how could it just be canceled out?