Water is filled in a tank, using a pipe such that after each 1 minute water level rises by 2 cm. Keerthi started measuring the height at 9:45 am. At 9 : 47 am, height of water was 23 cm. What was the height of water level at 9 : 40 am ?
1
9 cm
2
10 cm
3
11 cm
4
16 cm