a. The sum of three numbers is 81. The second number is twice the first. given that the third number is 6 more than the second, find the numbers.

 

b. Give me the points P(3, 5) and Q(-5, 7) on the Cartesian plane such that R (x, y) is the midpoint of PQ, find the equation of the line that passes through R and perpendicular to line PQ.