Heya!!!
Answer to your question:
Let no. of hours Joshua works be x
no. of he makes be y
Money he earns=9x+6y
According to question,
9 (8)+6y>155
72 +6y>155
6y>155-72
6y>83
y>83/6
y>13.8
So, Joshua must do atleast 14 deliveries to reach his goal.
Hope it helps ^_^