The sum of interior angles of any polygon is:
s=180(n-2)
Since we are dealing with a triangle:
s=180(3-2)
s=180°
That is, the sum of angles of any triangle is 180°.
In this case we are given two angles with measures of 32° and 102° so
a+b+c=180
32+b+102=180 combine like terms on left
b+134=180 subtract 134 from both sides
b=46°