PLS HELP (will mark brainliest)

A line passes through the points P (2 , 5) and Q (4 , a). Given that the point R (b , 9) is the midpoint of PQ,
1) Find the value of a and the value of b
2) Find the equation of the line that passes through the points (2 , 3) and (1 , 7)
3) the point (4 , h) lies on the line with equation y= 5 - 2x ,find h.