Let P = number of dozen peanut butter cookies sold.
Let C = number of dozens chocolate chip cookies sold.
Number equation: P = 85 + C
Value equation: 6.50P + 9.00C = 4055.50
Substituting the first equation into the second:
6.50(85 + C) + 9.00C = 4055.50
552.50 + 6.50C + 9.00C = 4055.50
552.50 + 15.50C = 4055.50
15.50C = 3503.00
C = 226
P = 85 + 226 = 311