Question 1209715
<pre>
 Go to https://www.wolframalpha.com/

Type in:    2*7^3 + a*7^2-23*7 + c = 0, 2*12^3 + a*12^2 - 23*12 + c = 0

Press ENTER

Get a = -531/19,  c= 16044/19.

So you have the second part of the problem (a,c) = (-531/19, 16044/19)

Now erase what you typed in before.

Type in:   2x^3 + ax^2 - 23x + c = 0, a = -531/19,  c= 16044/19

Press ENTER

See the third root: x = -191/38

Edwin</pre>