Which one is correct

What does the word submerged mean in the following sentence? after it rained for three days in a row, the streets were completely submerged.

Why is the improved education of girls so important, especially with regard to economics and health? what are the leading causes of death among teenage girls in africa and how are they tied to education?

Find the equation of the line passing through the point (–1, 5) and perpendicular to the line 3x + y = 4.