175 hours, he walked for 7.5 minutes. When do you want to walk for another 4.5 minutes?

7.5 minutes =0. 125 hours, 4.5 minutes =0.075 hours.

X hours later, just right.

175.125/175 = (x+0.075)/x (equal ratio)

The solution is x= 105.

Adding 105 hours on July 29th is 9: 00 on August 2nd.