Hi guys, I have been solving some problems recently, but there are few problems on which i am stuck:

1) If (a/b)-a=6 what is the value of sqrt of ((a+ab-2b)/b)?

2) For positive interger p,t,x, and y, if p^x=t^y and x-y=3, which of the follwoing cannot equal t?

a. 1 b.2 c.4 d. 9 e. 25

3)If a,b,c are distinct positive intergers and 10% of abc is 5, then a+b could equal...

a.1 b.3 c.5 d.6 e.25

I fully appreciate your help!