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Which values for a and b will create infinitely many solutions for this system of equations? ax-y=8 2x+y=b

What is the maximum total area that 450cm of string can enclose if it is used to form perimeters of two adjoining rectangles as shown?

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