Is BC=2.3 one of the options?
For that question, you can use the cosine rule, where;

In this case, we have..

Solving for BC with this will get you 2.250406, rounded off to the tenth is 2.3.
Step-by-step explanation:
½ [cos(a − b) − cos(a + b)]
Using sum and difference formulas:
½ [cos a cos b + sin a sin b − (cos a cos b − sin a sin b)]
Distribute the negative:
½ (cos a cos b + sin a sin b − cos a cos b + sin a sin b)
Combine like terms:
½ (2 sin a sin b)
Simplify:
sin a sin b
Right triangle
so
n + n + 40 = 90
2n = 50
n = 25
answer
Measure of angle n = 25°