X - 2/3 = 5/6
х = 5/6 + 2/3
х = 5/6 + 4/6
х = 9/6 = 1 3/6 = 1 1/2
a × 0,4 = 4/15
0,4а = 4/15 |÷0,4
0,4а ÷ 0,4 = 4/15 ÷ 4/10
а = 4/15 × 10/4
а = 4/15 × 5/2
а = 2/3 = 0,6
x - 5/8 = 5/8
х = 5/8 + 5/8
х = 10/8 = 5/4 = 1 1/4
9/10 ÷ с = 3/20
9/10 × 1/с = 3/20
9/10с = 3/20
9×20 = 3×10
180с = 30
с = 6