Where x is months and y is the amount left in the account y=-18x+550

Answer 1

The account started with $550 (the value of y at x=0; this is the y-intercept).

The value of the account is reduced $18 for each month later [ so, y lessens by ($18/mo) for each x month ]

At the end of each MONTH, the balance left in the account is:

month amount

0 550

1 530

2 514

. . . . . .

29 28

30 10

Thus, at the end of 30 months, there is only $10 left in the account, and another withdrawal of $18 will not be allowed.

Answer 2

You got

0 = -18x + 550

-550 = -18x

x = -550/-18 = 275/9 = 30 and 5/9 = 30.5

Roughly 30 and 1/2 weeks left