a)
2 5/15x + 1 1/15x = 6 4/5
3 6/15x = 6 4/5
3 2/5x = 6 4/5
x = 6 4/5 : 3 2/5
x = 34/5 * 5/17
x = 2
=============
( x - 3/5x) * 1 1/24 = 1 1/6 + 1 3/4
2/5x * 1 1/24 = 1 2/12 + 1 9/12
2/5x * 1 1/24 = 2 11/12
2/5 = 2 11/12 : 1 1/24
2/5x = 35/12 * 24/25
2/5x = 14/5
x = 14/5 * 5/2
x = 7