Can someone ? full explanation will me understand this better.

Okay so if two shapes are congruent that means they have the exact same measurements. 

So in the figure above, there are two triangles. Both of the triangles have one side that is 15 units long, and another side that is 5 units long. So now we just have to find out if the third side for both triangles are the same. And if you look at the figure the two triangles are both sharing the third side in the middle. Which means both triangles have the same measurement for the third side, making these two triangles congruent.

Hey Gary!

For any two items of comparison to be congruent, they must be of same size and same shape. If they do not meet those requirements, they are NOT congruent.

Let's look at our shapes.
They both are triangles, so they are the same shape.

Let's look at the size.
Line DC is congruent to Line AB.
Line DC has a length of 5 units.
Line AB has a length of 5 units.
Line DA is congruent to line BC.
Line DA has a length of 16 units.
Line BC has a length of 16 units.

Your answer is:
Yes, triangle ABC and triangle CDA ARE congruent.

If you need an equation, it would be y=2x+8, y would be how long it grew, x being weeks.if you need how long he was asleep, it would be 4 weeks if he started with no beard, the equation would be x=8÷2if he did have a beard before hand, the equation would be 2w+x=8