21) You most likely mean the number 0.666…. If x = 0.666…, then
10x = 6.666…
10x - x = 6.666… - 0.666…
9x = 6
x = 6/2 = 2/3
22) You either mean 1.2555… (only 5 repeats) or 1.252525… (both 2 and 5 repeat).
If x = 1.2555…, then
10x = 12.555…
100x = 125.555…
100x - 10x = 125.555… - 12.555…
90x = 113
x = 113/90
Otherwise, if x = 1.252525…, then
100x = 125.252525…
100x - x = 125.252525… - 1.252525…
99x = 124
x = 124/99
23) You either mean 0.4555… or 0.454545….
If x = 0.4555…, then
10x = 4.555…
100x = 45.555…
100x - 10x = 45.555… - 4.555…
90x = 41
x = 41/90
Otherwise, if x = 0.454545…, then
100x = 45.454545…
100x - x = 45.454545… - 0.454545…
99x = 45
x = 45/99 = 5/11