\[7\frac{1}{4} + 13\frac{7}{8} + 15\frac{3}{4} + 17\frac{1}{8} =\]
\[= \left( 7\frac{1}{4} + 15\frac{3}{4} \right) + \left( 13\frac{7}{8} + 17\frac{1}{8} \right) =\]
\[= 23 + 31 = 54\]