Okay. So as you probably know, area is l * w. 10 * 5 is 50, so the original area is 50 square feet. With each side being increased equally, after that is done, the area is 84 square feet. If you know basic multiplication, 12 * 7 is 84. 12 - 10 is 2. 7 - 5 is 2. That number being added is the same for all sides. The amount added to each side is 2 feet.
21.2264 is 21.2 rounded to the nearest tenths; the place after the decimal is there tenths place so in the hundreths place, the number 2 is less than 5 therefore rounding it to 2.
