NEED HELP ASAP

1. In a parallelogram a diagonal of the length 20 cm is perpendicular to one of the sides. Find the longer side of parallelogram if its perimeter is 80 cm.

2. The square root of number that is two bigger than k is twice as big as the square root of the number one less than k. What is k?

3. Find two consecutive numbers if the square root of the smaller number is 3 less than the bigger number.

Please give good explanations