Answer:
y = 20 + 35x
Step-by-step explanation:
Since it is a linear function, it can be written simply as y=mx+b (or y=b+mx), and if the slope is 35, (we can tell because that is the cost per month for service) then we know that the term will be 35x. We also can tell that the y-intercept is 20, because that is the starting fee.
Because of this, the situation can be represented with the expressions:
y = 35x + 20
and/or
y = 20 + 35x