Firstly, you have to add the two parts together to get a total,
4+5=9
You've then got to divide 126 by 9 to find out what one part is worth.
126/9= 14
Therefore, one part is 14.
To find what each is worth, you have to multiply both parts by 14.
14x4= 56
14x5= 70
(Just add these together to check that they're correct)
56+70= 126.
Therefore, 126 divided to the ratio of 4:5 is 56:70
Hope this helps :)