Answer:
C. 4.2a + 0.8
Step-by-step explanation:
Given:
The two binomials given for addition are:
and 
Now, adding both the binomials, we get:

Distributing the positive sign inside the second binomial, we get:

Now, combining like terms using the commutative property of addition, we get:

Simplifying the above expression, we get:

Therefore, the resulting addition of the given binomials is 
Hence, option C is the correct answer.
It is $6 more now than before...maybe you were looking for percent increase?
%change=100(final-initial)/initial
%change=100(10-4)/4=150% increase