These days, scientists all over the world use a standard system of measurements. It's the SI or metric system.
What about scientists in the United States, Liberia, and Burma ?
These three countries are the only ones in the world that haven't
adopted the metric system. What do THEY do ?
Easy. When scientists in those countries are off work, they use the
inches, yards, feet, quarts, miles and gallons that everybody around
them is using. But when they go to work, they use the same metric
system that everyone else in the world is using.
It is often revealed <span>at the resolution of the story, when the reader can see how the story ends.</span>
Let height of twin falls = x
height of seven falls = 2.5x
x + 2.5x = 420
3.5x = 420
x = 420/3.5 = 120
so twin falls = x = 120 ft
seven falls = 2.5x = 300 ft
what do you need , i mean your help , let me see if i can help