Hello, Rimas!
TKHunny has the best approach . . . graph it.
Consider: .$\displaystyle x^2 4 \:=\:c$
A) Find a value of c for which this equation has four soluions.
B) Find a value of c for which this equation has three soultions.
C) Find a value of c for which this equation has two solutions.
D) Find a value of which this equation has no solutions.
E) Are there any possble numbers of solutions of this equation?
$\displaystyle y \:=\:x^24$ is an upopening parabola.
. . It has xintercepts (±2, 0) and yintercept (0, 4).
The absolute value says: anything below the xaxis is "reflected upward".
So the graph looks like this: Code:

*  *

4*
* *  * *
*  *
* *  * *

    *   +   *   
2  2
Now cut the graph with a horizontal line $\displaystyle y \,=\,c$
. . and see where you get 4, 3, 2, or 0 intersections.