Do you have a question about it ?
What you need to do is give these problems a common denominator. Which makes 3/21 and14/21 respectively. Logically, you need to walk 4/21 of the trail. This can’t be simplified further.
Let's take a peek at the denominators first off, and do a "prime factoring" on them.
25 = 5 *
527 =
3 *
3 * 3
45 =
3 *
3 *
5
the numbers in bold are repeated there more than once among the factors, and therefore we'll use them once, so our LCD will be 5 * 5 * 3 * 3 * 3, or 675.