Answer:
Step-by-step explanation:
Obviously, all multiples of 3 and 7 can be paid.
1 cent can be added by adding a 7-cent stamp and taking away two 3-cent stamps. 2 cents can be added by adding three 3-cent stamps and taking away one 7-cent stamp. Hence any value more than 7 +2(3) = 13 cents can always be accommodated.
Amounts that are impossible:
1, 2, 4, 5, 8, 11 cents
All other positive integer amounts are possible.
-2;12
it's too easy!
9. -5(4+6r)
-20-30r
-20-30(4)=-20-120=-140
10. -9-n/3
-9-9/3=-9-3=-12
answers: -140, -12
Answer = 350