When you cannot simplify it further. The terms have no common factor besides 1 and A plus C does not have two numbers that multiply to the total and equal C.
Here the line passes through (0,0) and (1,3).
First we need to find the slope , and for that we need to use the following formula

On substituting the values from the point, we will get

Now we will use slope intercept form, which is

Where m is the slope and b is the y intercept
And on substituting the values of x and y from the point (1,3) and slope, m = 3, we will get


b =0
Substituting the values of m and b in the slope intercept form, we will get

Answer:
she will be taking 3600 mgs. in 90 days
Step-by-step explanation:
if she is taking a 20 mgs. twice a day that will make it 40 mgs. a day. If she takes it for 90 days
you will multiply 90 by 40
so
90
x40
= 3600 mgs. in 90 days
-1 = 3(5) + b
-1 = 15 + b
-16 = b
y = 3x -16
y - 5 = 3(x +1)