x:8/9=9/13;
13 * x = 8/9 * 9
13x = 8
x = 8 : 13
x = 8/13
7 1/5:x=9/10
9 * x = 10 * 7 1/5
9x = 10 * 36/5
9x = 72
x = 72 : 9
x = 8
