How do I completely solve f(a)+f(2a)=18a+10 ?

Question

I'm confused on the simplifying f(a)+f(2a).I could really use your help!!

Answer 1

f(x) = 6x+5

The notation f(a) is short for f(x=a).  Since x=a, just replace the x in f(x) with a:

 

f(x) = 6x + 5
f(a) = 6a + 5

 

Similarly, f(2a) is short for f(x=2a).  Since x=2a, just replace the x in f(x) with 2a:

 

f(x) = 6x + 5
f(2a) = 6(2a) + 5 = 12a + 5

So:

f(a) + f(2a) = 6a + 5 + 12a + 5 = 18a + 10     [Combine like-terms: 6a+12a=18a, 5+5=10]