You must manipulate the fractions so that they both have the same denominator. To do this, multiply the first fraction by 3 and the second by 4 so that they both have the denominator 12. The problem can then be written ((3(4x+1))/12)+((4(1-3x))/12) = (12x+3+4-12x)/12. To finish off the question, simplify the new numerator. This will give 7/12.