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2p = 1b (p=pencil; b=blue pen)
15= 10p + 5b
Now substitute using 2p=b
15 = 10p + 5(2p)
15 = 10P + 10p
15 = 20p
3/4 = p
pencils are $0.75 each
pens are 2p = 2*(0.75) = $1.50
Check your answer.
Is 10*0.75 + 5*(1.50) = 15?