Solve the system using elimination: me
12x - 8y = -12
6x + 4y = -30

12x - 8y = -12  

6x + 4y = -30

Multiply the 2nd equation by 2, to make the Y coefficients opposite:

6x + 4y = -30 x 2 = 12x + 8y = -60

Now add the two equations:

12x -8y = -12 + 12x +8y = -60

=  24x = -72

Divide bothe sides by 24 to solve for x:

x = -72/24

x = -3

Now replace x with -3 in the first equation to solve for y:

12(-3) - 8y = -12

-36 - 8y = -12

Add 36 to each side:

-8y = 24

Divide both sides by -8 to solve for y:

y = 24 / -8

y = -3

X = -3 and y = -3

(-3,-3)

1 number

if we use a graphing calculator, there is only one such number that satisfies the conclusion of the mean value theorem, that is, a number such that

where the right-hand side is the average rate of change of f on the interval [0.5,0.75], which is the slope of the secant line.

in the attached graph, the black line is the secant line which has its slope as the average rate of change of f on [0.5,0.75], while the orange line is the only tangent line to the graph of f in the interval that satisfies the mvt conclusion.