8/15*(9/4a -15/2b)-7/30*(16/7a-60/7b)=

Упростим.

8/15 * (9/4 * a - 15/2 * b) - 7/30 * (16/7 * a - 60/7 * b);

Скобки раскроем и сократим дроби.

8/15 * 9/4 * a 8/15 * 15/2 * b 7/30 * 16/7 * a + 7/30 * 60/7 * b;

2/15 * 9/1 * a 8/2 * b 16/30 * a + 60/30 * b;

2/5 * 3 * a 4 * b 8/15 * a + 2 * b;

6/5 * a 4 * b 8/15 * a + 2 * b;

Сгруппируем.

(6/5 * a 8/15 * a) + (2 * b 4 * b);

a * (6/5 8/15) + b * (2 4);

a * (18/15 8/15) + b * (-2);

a * 10/15 2 * b;

10/15 * a 2 * b;

2/3 * a 2 * b.