Let
c --------> the total cost
d -----> the number of days
we know that
The linear equation in slope intercept form is equal to
y=mx+b
where
m is the slope or unit rate
b is the y-intercept or initial value
In this problem
The slope or unit rate is equal to $50 per day
The y-intercept or initial value is equal to $100
so
substitute the given values
c=50d+100
answer option C