Step-by-step Answer:
AN is height, so A is perpendicular to BC. (See image attached).
BN = 18
AN = 24
AC = 40
All as labeled.
ABN is a right triangle, with AB = sqrt(18^2+24^2)=sqrt(324+576)=30
ACN is a right triangle, with CN = sqrt(40^2-24^2)=sqrt(1600-576) = 32
=>
BC = BN + NC = 18 + 32 = 50
