Given number of hours worked:
Monday = 5 hours
Tuesday = 3 hours
Wednesday = 4 hours
Thursday = 3 hours
Friday = 4 hours
Part A)
To find the total number of hours worked during the week, sum up the number of hours worked from monday to friday:

Katrina worked a total of 19 hours during the week
Part B)
To find the gross earnings for the week, since she is paid $15 per hour, her gross earnings will be:

Her gross earnings for the week will be $285
Part C)
In part A, the number of hours she worked during the week(from Monday to Friday) were added together in order to get the total number of hours worked during the week. In part B, her payment rate per hour was multiplied by the total number of hours she worked during the week to find her gross earnings for the week.