a) k + m < l + m

Hint: You're allowed to let any of those cardinals be finite or infinite in order to contradict the above.

b) k*m < l*m

Hint: You're allowed to let any of those cardinals be finite or infinite in order to contradict the above.

c) m^k < m^l

Hint: Let m = 0. Then find suitable k and l to contradict the above.

Or another approach:

Hint: You're allowed to let any of those cardinals be finite or infinite in order to contradict the above.