To get 75 using 7, 5, 6, and 3 only once:
= (7+5) * 6 + 3
parentheses first
= 12 * 6 + 3
multiplication before addition
= 72 + 3
= 75
Without being given any constraints, I'm assuming multiplication and addition were allowed.
Hope this helps! :)
Subtract the exponents when the base number is the same.
2 - 7 = -5
So 9^-5 or 1/9^5.
The answer to the question
Hello!
Out equation is: 
A= 6000
P=5000
N=1
T=5
R= What we are trying to find
This means we will have 
Divide both sides by 5000:

Move the power to the other side by rooting both sides:

Subtract 1 from both sides:

Now we just need to calculate: R = 0.03713728...
I don't know how many decimal places you can have, but I will round to 2. This will give you an Interest Rate of 3.71%.
I hope this helps! :)