Question 192256
An office has some 20 cent stamps and some 28 cent stamps. All together the office has 140 stamps for a total value of $31.20. How many of each stamp does the office have? 
my try: 
Stamps Number Value Total Value 
20 cent x .20 .20x
28 cent 140 -x .28 .28(140-x) 
.20x + .28(140-x) = 31.20 
.20x + 39.20 - .28x = 31.20 
.08x + 39.20 = 31.20
-.08x = -8.00
x = 800/8 =100