Answer: 3ml:4ml:7ml
Step-by-step explanation: To simplify ratios you have to find the highest number that you can divide all the parts in the ratio by (AKA as highest common factor)
In this case the common factor of 18,24 and 42 is 6.
so now divide all the parts by 6:
18/6=3
24/6=4
42/6=7
finally put these numbers back into the correct ratio format and for this question put on the units.
final answer= 3ml:4ml:7ml