Answer:
$120
Step-by-step explanation:
y = mx + b
The $100 sign up fee is a set amount, or the b value.
The $20 would be the m value since it the constant change, or the slope.
Thus, the equation would be y=20x + 100
The membership fee for 1 month would be --->
y= 20(1) +100
y= 20 + 100
y= $120