Explanation:
you need to have or create a coordinate grid with x and y coordinate axis (crossing each other at a right angle in the center).
you got 2 data points (2 bags of cherries with their weight and price).
a proportional (or linear) relationship is graphed as a straight line that goes through these 2 points.
the x axis (left-right) stands for the weight, the y-axis (up-down) stands for the price.
we see, when the weight goes up by 0.7 pounds (from 2.1 to 2.8), the price goes up by $2.66.
the slope of the line is
y-diff / x-diff = 2.66/0.7 = 3.8 = 38/10 = 19/5
the general equation of a line is
y = ax + b
a being the slope, b being the y-intercept (the y-value when x = 0).
we know now
y = 19/5 x + b
we use the coordinates of one point to get b :
7.98 = 19/5 × 2.1 + b = 7.98 + b
b = 0
our line equation is therefore
y = 19/5 x
since the original data coordinates are not nice numbers for a grid of whole numbers, let's find now 2 good points to mark on the grid and draw the line.
one point : x = 0. that gives us y = 0. so, (0, 0).
another point : x = 5. that gives us y = 19.
so, mark the points on your coordinate grid
(0, 0) means x = 0, y = 0 (the point where the 2 coordinate axis cross).
(5, 19) means x = 5, y = 19. or if you don't have that much space in the y direction, we can divide both coordinates in half (we can do that because this is proportional or linear) and get
(2.5, 9.5), and you mark this point instead (you can mark half-units with sufficient accuracy).
and then you draw a line through both points (extending beyond the points).