Rhonda bought her son an inflatable pool for the summer. it took her 20 mins to fill the pool to a depth of 6 in. what is the unit rate per minute(in per minute)
what is the unit rate per inch(mins per in)

Per means one. So this asks for in one minute, and in one inch.
20 minutes = 6 inches.
So dividing by 20 gets you one minute.
1 minute = 6/20 inches
1 minute = 3/10 inches

20 minutes = 6 inches.
So dividing by 6 gets you one inch.
20/6 minutes = 1 inch
10/3 minutes = 1 inch

(20 c 7) = 20*19*18*17*16*15*14/(7*6*5*4*3*2*1)
= 77,520