Answer:
4
Step-by-step explanation:
If the slope is 0, the line is horizontal and the y-coordinate is 4 for all x values.
Thus the missing y-coordinate is 4.
I think in this situation the best method would be a guess and check. You know that there are 8 dimes more than there are nickels. So just keep increasing each number by one until you reach $1.40. If there were 9 dimes and 1 nickels it would add up to $0.95. If there were 10 dimes and 2 nickels, it would add up to $1.10. If there were 11 dimes and 3 nickels, it would add up to $1.25. If there were 12 dimes and 4 nickels, it would add up to $1.40. So your answer is 12 dimes and 4 nickels.
I hope this helped!
For this case we must solve the following system of equations:

To solve we follow the steps below:
We multiply the second equation by -3:

Thus, we have the equivalent system:

We add the equations:

We look for the value of the variable "y":

Thus, the solution of the system is given by:

Answer:

4 for part A
17 for part B