We can use the Law of Sines to solve this, which states that [tex] \frac{sinA}{a} = \frac{sinB}{b} = \frac{sinC}{c} [/tex]. We can name the triangle like the one below to see that [tex] \frac{11}{sin40} = \frac{b}{sin81} [/tex]. We move the 11 up to sin81 to get that [tex] \frac{11sin81}{sin40} [/tex], which simplifies to 17 (rounded).
:)
