So, initially 240\(\frac{3}{8}\) -212 \(\frac{12}{3}\) were empty:
this is :
\(240 \frac{3}{8} - 212 \frac{12}{3} = 240 \frac{3}{8} - 212 +4 = 240 \frac{3}{8} - 216= 24 \frac{3}{8}\)
12/4 is 4 so that's why i substituted it with 4.
now, later 27 1/3 were used so we add this tho the original empty space
\(24 \frac{3}{8}+ 27 \frac{1}{3}\) = \(24 \frac{9}{24}+ 27 \frac{8}{24}\) = \(51 \frac{17}{24}\)
which is the result!