3a. Jackson's gross pay for 40 hours is
(40 h)×($12.20/h) = $488.00
3b. An equation for Jackson's pay could be
372.10 = h×12.20
This can be solved for h by dividing by 12.20
372.10/12.20 = h = 30.5
Jackson worked 30.5 hours last week.
3c. The total of hours shown is
(8) + (7 1/4) + (8 1/2) = (8 +7 +8) +(0.25 +0.50) = 23.75
The number of hours missing is the difference between this number and the hours found in part (b).
30.50 - 23.75 = 6.75
There are 6 3/4 hours missing from Jackson's time sheet for last week. This is less than a full day's work, so seems reasonable.
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Of course, you know the decimal - fraction conversions:
1/4 = 0.25
1/2 = 0.50
3/4 = 0.75