Answer:
post cards cost .06 each and envelopes cost .08 each.
Explanation:
Let p = the cost of the post cards
Let e = the cost of the envelopes
15p + 10e = 1.70
e = p + .02 Substitute p + .02 for e in the first equation
15p + 10(p + .02) = 1.70 Distribute the 10
15p + 10p + .2 = 1.70 Combine like terms
25p + .2 = 1.70 Subtract .2 from both sides
25p = 1.50 Divide both sides by 25
p = .06
Post cards cost .06 each.
Envelopes cost .08 each