Answer is choice B)
a = 74 because angle TRS and angle TMN are corresponding angles
The 40 and 34 degree angles add to 40+34 = 74 which makes up angle TMN
TRS and TMN are corresponding angles because they are on the top side of the horizontal line RS and MN respectively; also they are on the right hand side of the transversal line TM. In short, the two angles are in the upper-right corner of each intersection. That's why they are corresponding.