you have to make the denominators the same number so 12 because 3x4 is 12so you will have to multiply the numrator and the denominatorand then add them
[tex]\bf \cfrac{1}{3}+\cfrac{1}{4}\implies \stackrel{\textit{our LCD will be 12}}{\cfrac{(4)1+(3)1}{12}}\implies \cfrac{7}{12}[/tex]
