In a family of four, it is unlikely that all four people would be wage earners. Also, an hourly pay rate of $7.25 would be the gross, not net pay, of any worker as taxes are always deducted from gross wages.
However, assuming that the wage earners work 40 hours per week, we can calculate their gross wages as follows:
$7.25/hour x 40 hours/week = $290/week
1 wage earner would earn $20,650 in 71.2 weeks
2 wager earners would earn $20,650 in 35.6 weeks
3 wage earners would earn $20,650 in 23.7 weeks
4 wage earners would earn $20,650 in 17.8 weeks