Skater A (45 kg) and skater B (60 kg) push each other apart on smooth ice with 180 N for 0.5 s…

Step 1. (a) A: $\dfrac{180\ \text{N}}{45\ \text{kg}} = 4\ \text{m/s}^2$. B: $\dfrac{180\ \text{N}}{60\ \text{kg}} = 3\ \text{m/s}^2$.

Step 2. (b) A: $4\ \text{m/s}^2 \times 0.5\ \text{s} = 2\ \text{m/s}$. B: $3\ \text{m/s}^2 \times 0.5\ \text{s} = 1.5\ \text{m/s}$.

Step 3. (c) A, the lighter one: the same force gives a lighter body more acceleration.