The first line in this quesiton involves factoring everything on the top and bottom of the fractions.

Now, for the top of the first fraction:

2x² − 18 = 2(x² − 9)

We recognise the expression in brackets to be a difference of 2 squares, which we learned about before. We can write:

x² − 9 = (x + 3)(x − 3)

The bottom of the first fraction also uses difference of 2 squares:

x³ − 25x = x(x² − 25) = x(x + 5)(x −5)

The top of the second fraction requires taking the common factor of 3 outside:

3x − 15 = 3(x − 5)

The bottom of the second fraction has 2x as a common factor :

2x² + 6x = 2x(x + 3)

The third line involves cancelling out the following from top and bottom:

2
(x + 3)
(x − 5)

The final step is to multiply tops and multiply bottoms, since we cannot cancel anything else.