What are the steps to find the value of b ?

The angles should add to 540, so
b+ (3/2)b+(b+45)+(2b-90)+90=540

First combine like terms
5.5b+45=540

Then subtract 45 from both sides
5.5b=495

Divide both sides by 5.5
b=90

Final b=90

“exterior angles of triangles. an exterior (or external) angle is the angle between one side of a triangle and the extension of an adjacent side. try this drag the orange dots on any vertex to reshape the triangle.” look to get to the answer i explained what it means and other things i hope it you .