The factors of 45 are 9 and 5.
A number divisible by 45 needs to be divisible by both 9 and 5.
For a number to be divisible by 9 the sum of the digits must also be divisible by 9 and the number needs to end with either a 0 or a 5 to be divisible by 5.
This means the number needs to end with the 0 so cross out the last number (4)
Now find a sum of 5 remaining numbers divisible by 9.
5 + 1 + 4 + 8 + 0 = 18 which is divisible by 9
Cross out 9,7 and the last number 4 to get the number: 51480