Answer: B. (1)
Step-by-step explanation: On the first day, Phil used 1 gallon of paint and Lindsey used 3 gallons of paint. Therefore, the total amount of paint they used on the first day is:
1 gallon + 3 gallons = 4 gallons
To find how many gallons of paint were left after the first day, we need to subtract the amount of paint used on the first day from the original amount of paint:
5 gallons - 4 gallons = 1 gallon