If you would like to know what is the rate you are laying cement in bags per hour, you can calculate this using the following steps:
20 minutes ... 1/4 of the bag
1 hour = 60 minutes ... x = ?
20 * x = 1/4 * 60
20 * x = 15 /20
x = 15/20
x = 3/4 of the bag
Result: After 1 hour (= 60 minutes) of laying down the cement, you will use 3/4 of the bag.
If you would like to know what is the unit rate, you can calculate this using the following steps:
20 minutes ... 1/4 of the bag
x minutes = ? ... 1 bag
20 * 1 = x * 1/4 /*4
20 * 4 = x
x = 80 minutes
Result: After 80 minutes, you will use 1 bag.