Is 28 miles per hr is faster then 19 knots per hr?

Answer 1

No. The two units are not comparable. Miles per hour is a speed. Knots per hour is an acceleration.

However, I think the question was wrongly phrased and by knots per hour the question actually meant just knots (nautical miles per hour.)

A nautical mile is longer than a mile: 1 nautical mile = ~1.15 miles. So 19 knots = 1.15 * 19 miles per hour = 21.85 mph.

The answer is: Yes (if by knots/hr the question really meant knots)

or

No (if the question was initially correctly phrased.)