If you can calculate simply, you should calculate simply. (1 / 13 + 1 / 16) × 13 × 16 12 × (1 / 3 + 1 / 2 + 1 / 6)

(1 / 13 + 1 / 16) × 13 × 16
=1 × 13 × 16 of 13 + 1 × 13 × 16 of 16
=16+13
=29
12 × (1 / 3 + 1 / 2 + 1 / 6)
=1 / 12 × 3 + 1 / 12 × 2 + 1 / 12 × 6
=4+6+2
=12