24: 40 in equivalent ratio 12: ? ? : 80 what is the answer then i dont get it

The first thing we have to do is to simplify the ratio. To do this, we must divide both numbers (24 and 40) by the Highest Common Factor. 
In this case, the Highest Common Factor is 8

When we divide both of these numbers by 8, we get the simplified ratio of 3:5

For the first question, we must work out what number has been multiplied with 3 to get 12. The answer is 4. So to work out the other number of this ratio, we must multiply 5 by the same number, 4. So, we get 20
So this ratio becomes 12:20. To double check it is correct, we should be able to get back to the 3:5 ratio, which we can. 

For the next one, we must decide which number 5 was multiplied by to get 80. 80/5 = 16, so the multiplying factor is 16

To work out the first number in the ratio, we must multiply the 3 by 16, so we get 48
So, the second ratio will be 18:80

Sorry if it doesn't make much sense, don't hesitate to ask any questions!
Hope I helped!! xx