Answer:
26.833
Explanation:
So I provided a diagram assigned the sides to a variable to make it a bit easier to refer to the sides.
The essence of this problem is going to be Pythagorean Theorem which is a relationship between the sides in a right triangle as follows:
where c=hypotenuse
So let's solve for "A" using the Pythagorean Theorem to represent it:

Btw the reason I used "24" is because I know the length of the entire line is 30, except the side I'm not counting in this is 6 since it's not part of the triangle.
Now let's solve for A^2:

Now represent "B" using the entire triangle:

We also know that:
by using the triangle in the top right that's formed using A, B, and 6.
You might now see where this is going. Now let's plug in these representations of A^2 and B^2 into this last equation:
Original Equation:

Equations we will use for substitution:


Now let's plug these in for A^2 and B^2


Now let's combine like terms:

Now let's move it all to one side

We can use the quadratic formula to solve this and get the following solutions:

We can reject the negative solution based on the context thus leaving us with the solution: 26.833