If this is represented by a linear function, then we know that the amount of money decreases at an unchanging amount. Knowing this, and knowing that on day 8, she had 2400, we simply just add 2400 to 8 100's:
2400 + 8*100 = 2400 + 800
Carrie initially had $3200, or Option C.
A^2 + B^2=C^2 so there for the hypotenuse (13^2) - (5^2) will give you the last side
