A scale model of the Golden Gate Bridge in San Francisco has a main span that is 284 centimeters long. If the scale of the model is 1 cm : 15 ft, how long is the main span of the bridge?
We can use a proportion, here:
Let x be the main span length
15 ft/ 1cm = x ft / 284 centimeters cross-multiply
284 * 15 = x = 4260 ft
