It is telling you that a regular shower head’s water flow is 3.5 gallons per minute. Then it tells you that a low flow shower head’s water flow is 1.5 gallons LESS THAN the regular. Meaning that 3.5 - 1.5 = 2.
Her error is that she failed the subtract the low flow shower head’s gallons per minute from the regular shower head’s.
To find out the correct way is to subtract 3.5 - 1.5, which would then equal to 2.
On how much water would be used, you multiply 2 to the amount of total minutes the class used (180). Your answer is 360.
