In Euclidean geometry (the geometry you're probably familiar with), the interior angles of a triangle always add to 180°.
With that knowledge, we can set up an equation that lets us solve for x based on our given angles by setting their sum equal to 180.
[tex]3x+(2x-1)+46=180\\5x+45=180\\5x=135\\x=27[/tex]
To find ∠B, we simply substitute the x for 27:
[tex]2x-1=2(27)-1=54-1=53[/tex]
So, m∠B = 53°.