Step 1: Prime factors of 42 are 2, 3 and 7.

Prime factors of 60 are 2, 2, 3 and 5.

Step 2: $\frac{42}{60}$ = $\frac{2\times 3\times 7}{2\times 2\times 3\times 5 }$

Step 3: $\frac{42}{60}$ = $\frac{\not{2}\times \not{3}\times 7}{\not{2}\times 2\times \not{3}\times 5 }$

Step 4: $\frac{42}{60}$ = $\frac{7}{2\times 5 }$ = $\frac{7}{10}$

The fraction $\frac{42}{60}$ can be simplified to $\frac{7}{10}$.