First the common denominator has to be 6. So to get to 6 you multiply the 2 by 3 and the numerator by 3 giving 3 over 6 then you multiply 3 times 2 to get to 6 so the following fraction is 2 over 6. So when u add the two together it gives you 5 6ths
THIS ANSWER IS FOR f(3):
f(x)=x+3
f(3)=3+3
f(3)=6
THIS ANSWER IS FOR f(-2):
f(x)=x+3
f(-2)=-2+3
f(-2)=1