Answer:
Part a)

Part b) The cost to take classes every weekend (Saturday and Sunday) during the month of January is $140
Explanation:
Part a)
Let
x ----> the number of classes
y ----> the total cost
we know that
The equation of the line in slope intercept form is equal to

where
m is the slope or unit rate of the linear equation
b is the y-intercept or initial value of the linear equation
In this problem
The slope is equal to

The y-intercept is
---> annual fee
substitute

Part b) Use the equation from above and find out how much it would cost to take classes every weekend (Saturday and Sunday) during the month of January
we know that
During the month of January 2020 we have 8 classes (4 Saturday and 4 Sunday)
so
For x=8
substitute in the linear equation


therefore
The cost to take classes every weekend (Saturday and Sunday) during the month of January is $140