b Substitute 138 for f(x) in the function from Part A.
A
a f(x)=12 * x+42
B
b 8 days
Practice makes perfect
a Since the daily rental fee is 12 dollars, we know that the rate of change is constant every day. Therefore, we can write 12 as the slope of a linear function.
y= 12x+bAdditionally, the initial fee is a flat 42 dollars. This is paid once and is unaffected by the number of days we rent. This will be the y-intercept of our function. Now we can write the function in slope-intercept form.
y=12x+ 42
Since we want to write this equation using the symbols given in the exercise, we will replace y with the function notation f(x) and place a multiplication symbol between the slope and x.
f(x)=12 * x+42
b To find the number of rental days when the bill is $138, we solve for x when f(x)=138.
