Hi, I found out that it is easier to use 7^4=2401. It is now easy to see that 2400 is divided by 15, hence the reminder is 1. It is easier to see that 625 when dived with 4 gives a reminder of 1. Given that, 7^625 = ( (7^4)^x)*7 Let x be 624/4. We know that 7^4 / 15 leaves a reminder of 1. Hence (7^...