Mr. Smith wants to lose weight at a rate of 4 pounds per month. This is a negative rate (because he wants to LOSE weight).
The linear equation is written as:
y = mx + c
Where m is the rate or slope of the equation.
Therefore we know that m = -4 (The 4 is negative because it is a loss of weight as explained earlier)
y is the weight according to the question
x is the months according to the question.
c is the initial value of y. In this case, y is the weight; thus, the initial value of the weight is260 according to the question.
Therefore, the equation is:
y = -4x + 260
or
weight = -4 x month + 260
If he reaches 220 pounds, it means that the equation becomes:
220 = -4 x month + 260 .
subtract 260 from both sides
220 - 260 = -4 x month + 260 - 260
-40 = -4 x month
Divide both sides by -4
Therefore, number of months to reach 220 pounds is: 10 months.