Question 22983
Let the number of 20 cent stamps be "x"
Then number of 33 cent stamps is "75-x"
Value of 20-cent stamps is (20)x cents
Value of 33-cent stamps is (33)(75-x)= (2475-33x) cents
EQUATION:
Value of 20 cent + Value of 33 cent is 1995 cents
      20x +2475-33x = 1995
            -13x = -480
               x= 36.923...
This answer doesn't make any sense as you cannot have 
36.923... stamps.

Cheers,
Stan H.