2 Answers

By the way your question is:

4x / 13 + 3/ 13

= [4x  +3 ] / 13

Remember! when there is same denominator on the given fractions, we add or subtract the numerator to get the result

& the Unlike terms can never add up or be subtracted.

Hope this has helped you to some extent.

........................and the reason you cannot solve for "x" is because you do not have a complete equation.  The two fractions would need to equal something.  If you complete the equation (i.e. (4x + 3)/13 = 3 )      THEN you could calculate for "x"

(4x + 3)/13 = 39/13  (changed the whole number to a fraction)
(4x + 3) -3/13 = 39/13 - 3/13
4x/13 = 36/13
4x/13  (dvidied by 4/13)    =   36/13 divided by 4/13
x  = 36/13  X 13/4
x  = 468/52
x  =  9
(Now substitute 9 for x and see if you balance)
4(9) + 3/13 = 3
36 + 3/13 = 3
39/13 = 3
3 = 3        

whooooopeeeee