Whenever you sign a lease for an apartment, you typically have to pay a security deposit before you even move in; this is in case something happens while you care occupying the apartment and repairs have to be made. one apartment building has apartments that rent for $900 a month and a security deposit of $600. write an equation to represent the situation described. f(x) = 600x + 900 f(x) = 600x - 900 f(x) = 900x - 600 f(x) = 900x + 600

The answer is F(x) = 900x + 600

Let x stands for the number of months

The apartment is rented for $900 a month, so every month it will be paid 900x (for example, for one month (x = 1), you will pay 900 · 1 = $900, for three months (x = 5), you will pay 900 · 5 = $4500, etc.)

A security deposit is paid only once and is not dependent on the number of months. So, its value is only 600. 

These two values must be summed up because both must be paid, nothing is to subtract. Therefore, the function f(x) for  apartments that rent for $900 a month and a security deposit of $600 is:
f(x) = 900x + 600