His total sales were 402.68 dollars. 700 minus 275 minus 22.31
Write it out as a set of equation:
Let x be number of 8 cent stamps, y be 10 cent stamps, and z be 2 cent stamps.
x=y
z=x+y
8x+10y+2z=440
Lets first solve for x:
from x=y and z=2x(from first equation) the last equation is
8x+10x+4x=440
22x=440
x=20
know that x=20, you also know that y=20 as well, since z=x+y, z=40.
So 20 8-cent stamps, 20 10-cent stamps, and 40 2-cent stamps.
The answer to your question is 215
