His regular pay: 13*40 = 520
His overtime pay: (13*1.5)*5 = 19.5*5 = 97.5
His pay for the week: 520+97.5 = 617.5
In his regular pay, you just multiply the hours he worked by the pay he got per hour. In his overtime pay, you just multiply the pay per hour by time-and-a-half (1.5) and then by 5 hours he worked overtime. In the end, you just add all these numbers to get $617.5