Answer:
a) No equation/Contradiction
b) One Solution/Conditional
c) Infinite Solutions/Neither
Explanation:
a) you combine like terms: 7x+9=7x-8
then subtract 7x from both sides, since 9 isn't equal to -8 there is no solution that would make it a contradiction
b) Combine likes: 13x-7=12x+21
subtract 12 x: x-7=21
add 7: x=14
c) Combine like terms: -3x+24=-3x+24
24=24