Adding and subtracting fractions w/like denominators

To add or subtract fractions, what must be the same?

 $\frac{3}{4}$   $+$   $\frac{1}{4}$   $=$  

(a)  

 $\frac{7}{12}$   $-$   $\frac{2}{12}$   $=$  

(a)  

 $\frac{6}{17}$   $+$   $\frac{7}{17}$   $=$  

(a)  

 $\frac{15}{20}$   $-$   $\frac{6}{20}$   $=$  

(a)  

 $\frac{23}{30}$   $-$   $\frac{16}{23}$   $=$  

(a)  

 $\frac{27}{50}$   $+$   $\frac{17}{50}$   $=$  

(a)  

 $\frac{23}{40}$   $-$   $\frac{18}{40}$  

(a)  

 $\frac{32}{33}$   $-$   $\frac{19}{33}$   $=$  

(a)  

At the beach, Charlotte and her sister both built sandcastles and then measured their heights. Charlotte's sandcastle was 3/4 of a foot tall and her sister's was 1/4 of a foot tall. How much taller was Charlotte's sandcastle than her sister's?