Question 667977
Establish variables
x = pencils
y = pens
...
Given
2x+3y=.78
3x+2y=.72
...
Multiply the first equation by -3 and the second equation by 2
-3(2x+3y=.78)
2(3x+2y=.72)
to get 
-6x + -9y = -2.34
6x+4y=1.44
...
Add them together
-6x + 6x + -9y + 4y = -2.34 + 1.44
...
Combine like terms
-5y = -.9
Divide both sides by -5
{{{highlight_green(y = .18)}}} for the price of pens
...
Multiply the first equation by 2 and the second equation by -3
2(2x+3y=.78)
-3(3x+2y=.72)
...
to get
4x+6y=1.56
-9x-6y=2.16
...
Add them together
4x + -9x + 6y + -6y = 1.56 + -2.16
...
Combine like terms
-5x = .6
Divide both Sides by -5
{{{highlight_green(x = .12)}}} for the price of pencils
...
Check 
{{{cartoon(
2(.12) + 3(.18),
.24 + .54,
.78)}}}
{{{cartoon(
3(.12) + 2(.18),
.36 + .36,
.72)}}}
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