If the numerator and denominator in a fraction contain common factors, they can be crossed out. This is equivalent to dividing both numerator and denominator by the same number. $$\frac{2\cdot 3\cdot 4}{5\cdot 3\cdot 4}=\frac{2\cdot \cancel{3}\cdot \cancel{4}}{5\cdot \cancel{3}\cdot \cancel{4}}$$