Go with the order of operations which is PEMDAS Parenthesis Exponents Multiplication Division Addition Subtraction
The first thing you do is the exponents. 4^2=16. 5^3=125. Your new equation is 125-30/3+16. Now you do division since there isn't any multiplication. 30/3=10. Your new equation is 125-10+16. Addition is your next step. -10+16 is 6. Your new equation is 125+6. Your answer is 131. Ta-da.
I believe he dove 6 feet because started 3 feet below water and went down to 9 feet below water and the difference between 9 feet and 3 feet is 6 feet.
