What value of C is needed to complete the square?

x2 + 10x +c= -3+ c

The area of a rectangle is 15+5y square feet. which of the following expressions could be the length of the sides of the rectangle, in feet a. 5 and 3y b. 5 and 3+y c. 5 and 5+y d. 3 and 5+3y

5,600 x 10^3 = a) 560 b) 5,000,600 c) 5,600,000 d) 56,000

The area of square garden is 300m squared. how long is the diagonal?