y-intercept -3
slope 1/2
is sufficient info with which to write an equation for a straight line:
y = mx + b becomes y = (1/2)x - 3.
You should check this by determining whether or not (2,-1) satisfies this equation.
0.19880716 should be your answer
Sorry if wrong
The distance between a point

on the given plane and the point (0, 2, 4) is

but since

and

share critical points, we can instead consider the problem of optimizing

subject to

.
The Lagrangian is

with partial derivatives (set equal to 0)




Solve for

:


which gives the critical point

We can confirm that this is a minimum by checking the Hessian matrix of

:


is positive definite (we see its determinant and the determinants of its leading principal minors are positive), which indicates that there is a minimum at this critical point.
At this point, we get a distance from (0, 2, 4) of
You have to do 4 times the 8 which is 24. Then find the adding for the -6. 1*6 2*6 3*6 4*6 , 4*6 is 24 so your answer would be (x-4) (x+6)