Answer:
Step-by-step explanation: Let variable x represent the 15¢ stamps, and variable y represent 20¢ stamps.
x= 3y-8
0.15x+0.20y = 4
Replace x in the second equation by (3y-8)
0.15(3y-8) + 0.20y = 4
0.45y - 1.2 +0.20y = 4
Collect like terms;
0.45y+0.20y = 4+1.2
0.65y = 5.2
Divide both sides by 0.65 to solve for y;
y= 5.2/0.65
y = 8
Replace in equation " x=3y-8 " to solve for x;
x = (3*8) -8
x=24 - 8
x = 16
Therefore, the 15¢ stamps are 16 in number, and the 20¢ stamps are 8 in number.