If a test is 150 questions how many answers can you get wrong to still get an 80%

On an airplane there are two seats on the left side and three seats on the right side there are 90 seats o the right side of the plane

Bob is putting books on a shelf and takes a break after filling 18 1/2 inches on the book shelf. the book shelf is now 2/3 full. how long is the entire bookshelf?

Atrain leaves little? rock, arkansas, and travels north at 90 kilometers per hour. another train leaves at the same time and travels south at 80 kilometers per hour. how long will it take before they are 680 kilometers? apart?