Question

Suppose a+b = 2aa+b=2aa, plus, b, equals, 2,

Answer 1

B-a=0.

Starting from the original equation, 
a+b=2a

We can isolate b by subtracting a from both sides:
a+b-a=2a-a
b=a

Substituting this into b-a, we have
a-a = 0