Joe is 3 kg lighter than Chris, so Chris = Joe + 3. The total mass is both bars added.

Joe45 kgChris45 kg3?

Plain numbers are given; italic underlined numbers are worked out.

  1. Chris → 45 + 3 = 48 kg
  2. Total → 45 + 48 = 93 kg

The total mass of the two boys is 93 kg.

Check: 48 − 45 = 3 kg, and 45 + 48 = 93 kg. ✓