"Where d is the number of days she has worked that week"
Substitute d = 0, meaning she has worked no days yet. Then P = 108. Thus when she has worked no days yet, she has 108 phones to repair. Alternately phrased, Kathy starts each week with 108 phones to fix.
Substitute d = 0, meaning she has worked no days yet. Then P = 108. Thus when she has worked no days yet, she has 108 phones to repair. Alternately phrased, Kathy starts each week with 108 phones to fix.