Well, the inside angles of all triangles add up to 180°, so you come to this equation:
[tex](3x + 1) + (2x - 1) + 40 = 180[/tex]
Which can be simplified to:
[tex]5x + 40 = 180[/tex]
Subtract the 40 from both sides, then divide by 5 and you'll have X!
[tex]5x = 140[/tex]
[tex]x = 28[/tex]
Plug that X back into the equation for angle B, and solve
[tex]2(28) - 1 = 55[/tex]
Which is choice B
