A because, all the numbers multiplied by those factors equals their spot in the number
A:b=c:d
7.2:x=1:25. If u see two ratios equal each other, the product of a and d is equal to the product of b and c. This means that (7.2 times 25) is equal to x. This equals 180=x. The actual distance of the trail of 180 km. Hope this helps!
