If he multiplied the first equation by 5, that would give us:
10x + 45y = 205
Now we need to get -45y to eliminate the y-terms, So we divide -45 / 5 and we get -9. So we multiply the 2nd equation by -9.
(I'm assuming the first equation is actually 2x + 9y = 41, and not 2x + 9 = 41)