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cross section paralle to the base of a cone
diagonal cross section through the widest part of a sphere
diagonal cross section of a cylinder
shape created when a semi-circle is rotated about the y-axis
perpendicular cross section of a cone

The equations that are used to determine the values of x and y are 3x - y = 9 and 4x + y = 5. According to the degrees of freedom rule, the number of unknown variables should be equal to the number of independent equations in order to solve the problem. In this respect, we can use elimination in order to solve the equations

3x - y = 9
4x + y = 5

we add these two in order to eliminate y, thus,

7x = 14
x = 2 

from equation 1, 3*2 - 9 = y ; y = -3. hence the solution set is equal to (2,-3). The answer to this problem would have to be C.