Since the ratio is 10:3 we can find the total number of children and adults by finding how many times 13 (10+3) goes into 39. 39 / 13 = 3 so we can take the original 10:3 ratio and just scale it up to fit the whole group 10:3 * 3 -> 30:9:
From here it gets a little easier we know three adults of the 30 get off at the next stop bringing us to 27. So now our ratio is 27:9 we can simplify that down to 3:1 to get our final answer. Hope that helps!
