let's call
 x = number of hours worked by Kyle in his old job.
 y = number of hours worked by Kyle in his new job.
 Writing the system of equations:
 x + y = 54
 5x + 7y = 338
 Solving the system of equations:
 5 (54-y) + 7y = 338
 270-5y + 7y = 338
 2y = 338-270
 y = 68/2 = 34
 Therefore, Kyle worked 34 hours in his new job.