Question 22983
let $0.20 stamps be x and let the other be y
x+y=75
y=75-x
20x+33y=1995
20x+33(75-x)=1995
20x+2475-33x=1995
-13x=-480 (divide both sides by -15)
x=36
y=75-36 
y=39
Hence, the number of $0.20 were 36 stamps and for $0.33 there were 39 stamps.