10,8*(-4/9) + 21, 21:3 - 7 целых + 3/5

= 10.8 * (-4/9) + 21 + 7 - 3/5
= -4.8 + 21 + 7 - 3/5
= 16.2 + 7 - 3/5
= 23.2 - 3/5
= 23.2 - 0.6
= 22.6

Therefore, the final result is 22.6.