Answer:
b = 30
Explanation:
The sum of the 2 angles above the line will equal the angle below the line
3b + b - 15 = 2b + 45
4b - 15 = 2b + 45 ( subtract 2b from both sides )
2b - 15 = 45 ( add 15 to both sides )
2b = 60 ( divide both sides by 2 )
b = 30