To solve this you need to know that cosine∅ = adjacent/hypotenuse. We already know that hypotenuse = 5 and that ∅ = 70*. By substituting these in you will get cosine 70* = adjacent/5. Evaluate cosine 70* on the calculator and get 0.633... Multiply both sides by 5 and get adjacent is about equal to 3.1666. Because BC is the adjacent side of the triangle, this is the length of BC.
