Why do x and y have to be positive

The amount of money, in dollars, in an account after t years is given by a = 1000(1.03)^t. the initial deposit into the account was $_^a0 and the interest rate was _a1% per year. only enter numbers in the boxes. do not include any commas or decimal points^t. the initial deposit into the account was $__^a0 and the interest rate is % per year.

About 60% of the normal humanbeing's body weight is composed ofwater. how much of a 125 poundperson is water weight? f 72 pounds h 76 poundsg 75 pounds i 80 pounds

The parabola x = y² - 9 opens: a.)up b.)down c.) right d.)left