Answer:

Step-by-step explanation:
Given
The attached plot
Required
The line of the best fit using
and 
We have:


Calculate slope (m)




The equation is then calculated using:


Expand


0.7(5x+15)=2.9 -(x+3)
3.5x+10.5=2.9-x-3
3.5x+10.5= -0.1- x
4.5x= -10.6
x= -2.3555...
Check:
0.7(5(-2.3555...) +15) = 2.9 -(x+3)
2.2555... = 2.2555...
Answer:
31.25×
Step-by-step explanation:
suppose that the value of x was 3 . that would mean that they bought 3 calculators .
if one calculator is $31.25 then 3 would be $31.25× 3
the same rule would apply for x