Simple calculation of 2 / 3 △ 15 / 28 × 5 / 21

Simple calculation of 2 / 3 △ 15 / 28 × 5 / 21

2 / 3 △ 15 / 28 × 5 / 21
=2/3×28/15×5/21
=2/3×4/9
=8/27