The spending limit on John's credit card is given by the function f(t) = 15,000 + 1.57, where x is his monthly income. 1-13) $60,000, his monthly income is The variable x represents in the inverse function. If John's spending limit is​

1.
"The spending limit on John’s credit card is given by the function f(x)=15,000+1.5x"

means that if the monthly income of John is $ 5,000 ,he can spend at most

f(5,000)=15,000+1.5*5,000=15,000+ 7,500=22, 500 (dollars)

Or for example

if Johns monthly income is $8,000, then he can spend at most

f(8,000)=15,000+1.5*8,000=15,000+ 12,000=27,000 (dollars)

2.
Now, assume that the maximum amount that John can spend is y.

Then, y=15,000+1.5x

we can express x, the monthly income, in terms of y by isolating x:

y=15,000+1.5x

1.5x = y-15,000
X=y-15,000/1.5

thus, in functional notation, x, the monthly income, is a function , say g, of variable y, the max amount:
X=g(y) y-15000/1.5
since we generally use the letter x for the variable of a function, we write g again as:

G (x) x-15000/1.5
tells us that if the maximum amount that John can spend is 50,000 $, then his monthly income is 23,333 $.

3.

If John's limit is $60,000, his monthly income is
G(600,000)=60,000-15,000/ 1.5=45,000/1.5 =30,000

dollars.

$ 30,000

Remark: g is called the inverse function of f, since it undoes what f does.

instead of g(x), we could use the notation