First thing to know - remember that any number over itself as a fraction equals "1"
Now you have to create an improper fraction from the mixed number 4 1/2. Let me know if you have difficulties with this.
What happens if you multiply this new improper fraction by "1"? It stays the same. This is true, even if the numbers change. When we multiply a fraction by 2/2, or 5/5, or 198/198, we are multiplying it by "1" each time. The result is an "equivalent fraction"
EX.- 16/7 * 3/3 = 48/21
16/7 * 5/5 = 80/35
All of the equivalent fractions, 16/7, 48/21 and 80/35 are considered to be equivalent since they represent the exact same proportion, only divided into more sections.
Hopefully that helped!