Question 362437
Let's say pen = A, and pencil = B,

Bob >> A + 4B = $1.65

Joe >> 4A + B = $3.75

You have 2 unknowns and 2 equations. But you must need one unknown and one equation in order to solve this problem.Therefore you must wipe out one variable.For example I want to wipe out A therefore I Multiply the first(Bob's) equation by 4.

It looks like now:
Bob >> 4A + 16B = $6.6

Joe >> 4A + B = $3.75

You have to subtract Joe's equation from Bob's equation in order to wipe out A.

4A + 16B = $6.6

4A + B = $3.75
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0A + 15B = $2.85 Therefore you get 15B = $2.85 and you can find B as $0.19

and if you put B into any equation such as 4A + B = $3.75

you get 4A + $0.19 = $3.75 and when you solve this you get A as $0.89

RF.