The equation is in the description because it was too long

Question

the equation needs to be in y=mx+b

 Marty is spending money  The average rate of three dollars per day. After 14 days here $68 left. The amount less depends on the number of days it has passed. write in equation for this situation use your equation to find the amount of money he begin with. 

Answer 1

 

In y = mx + b, m is the slope, b is where the line hits the y-axis (called the y intercept).

 

The slope, m, is  -3.   This represents  -3 dollars/day  (minus because he is spending).  

 

If you picture the x-axis as time (number of days) and the y-axis as number of dollars Marty has, then you know the line will go through  (14,68).   Think about that:  y=68 when x=14.    These values can be used to solve y=-3x+b for  the unknown b.

 

Since they ask for the amount he had at the beginning (x=0),  b will also be the answer.

 

If they had asked for how much he had after some other number of days, you'd still solve for b but then you'd plug in the number of days for x.   For instance, once you have solved for b, how much does he have after 30 days?  [ $20 ]