First, line them up.
5 $${\frac{{\mathtt{1}}}{{\mathtt{4}}}}$$
+ 7 $${\frac{{\mathtt{1}}}{{\mathtt{2}}}}$$
————
Now, make the fractions into the Lowest Common Denominator. Then, add.
5 $${\frac{{\mathtt{1}}}{{\mathtt{4}}}}$$
+ 7 $${\frac{{\mathtt{2}}}{{\mathtt{4}}}}$$
————
12 $${\frac{{\mathtt{3}}}{{\mathtt{4}}}}$$
So, $$12\frac{3}{4}$$ is the answer.