Answer:
100
Step-by-step explanation:

The average cost represents the slope of the line of the graph.
Increasing the slope of the graph increases the steepness of the line.
Therefore,
increasing the average cost of gas from $1.50 to $2.20 will increases
the steepness of the line. (i.e. the line becomes closer to the vertical
line).
Number of students who have sent a text message only is given by the difference between those that have sent a text message and those that have done both.
i.e. Number of students who has sent a text message only = 58 - 12 = 46
Number of students who have uploaded a selfie only is given by the
difference between those that have uploaded a selfie and those that
have done both.
i.e. Number of students who have uploaded a selfie only = 21 - 12 = 9
The total number of students surveyed is 70.
Let the number of students who have neither sent a text message nor taken a selfie today be x, then
46 + 9 + 12 + x = 70
67 + x = 70
x = 70 - 67 = 3
Therefore, 3 students neither sent a text message nor taken a selfie today.
The number of students that have sent a text message or have taken a selfie today is given by the sum of the number of students that have sent a text message and the number of students that have taken a selfie less the number of people that have done both.
i.e. number of students that have sent a text message or have taken a selfie today = 58 + 21 - 12 = 67.
The equation would be y = 25x + 50
In order to find this equation, we need to know how much the gift from her grandparents was. To do so, we have to find out how much she's saved from dog walking.
Since she saves $25 a month for 7 months, we can find the total amount as:
25*7 = 175
Then we can subtract that from the total she has saved to find the amount for the gift.
225 - 175 = 50
Finally, we put the amount per month in the equation with the gift as the y intercept to create the equation above.