This question doesn't belong here but in pre-algebra or (analytic) geometry...anyway:
a)(i) Calculate the middle point of the segment AB: it is M .
(ii)Calculate the slope of the segment AB:
(iii) Calculate the equation of the line through M and perpendicular to AB: its slope must be , and then the line is
b) Evaluate the line on which the segment AB is and then solve the system of linear equations determined by this equation and the one you found in (a-(iii))