Find the distance, D, across the river. Assume that the ratio of d to 45 feet is the same as the ratio of 60 feet to 20 feet.
Let d be the distance across the river and let x be the distance from the starting point to the opposite bank of the river.
According to the given ratios, we can set up the equation:
d/45 = 60/20
Cross multiplying, we get:
20d = 45 * 60
d = (45 * 60) / 20
d = 135 feet
Therefore, the distance across the river is 135 feet.