A chemist has three different acid solutions. The first acid solution contains
20% acid, the second contains 35% and the third contains 80%. He wants to use all three solutions to obtain a mixture of 54 liters containing 55% acid, using 2 times as much of the 80% solution as the 35% solution. How many liters of each solution should be used?
The chemist should use liters of 20% solution, liters of 35% solution, and liters of 80% solution.

for finding the midpoint of any given 2 pair of points simply add the respective x coordinates with other x coordinate and the y coordinate with other y coordinate and divide them by 2

in your question it will be :

(3+1)/2 for the x coordinate of mid point i.e 2

[8+(-4)]/2 for the y coordinate of midpoint i.e 2

so coordinates of mid point of points (3,8) and (1,-4) will be (2,2)

b. 153 students do not participate in sports and seventy-five 12th graders were surveyed

she will travel a distance in the range of 3 - 11 miles