Answer:
b=6
Explanation:
One of the kinds special triangles you learn about are the Pythagorean triples. These are right triangles with sides in certain ratios. One of them has sides in the ratios 3:4:5.
More generally, this triangle has sides in the ratio 3x:4x:5x
In your triangle, the ratio 8:10 corresponds to 4x:5x with x=2. Therefore, the remaining side is 3x with x=2, so
b=6