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
Answer: C
Step-by-step explanation:

Find the least common denominator of 4, 3, and 12.
4-3-12 | 3
4-1-4 | 4
1-1-1 |-------- 12
The first fractions needs to be multiplied by 3, and the second fraction, by 4

Solve;

Add the fractions with positive signs and subtract the one with negative sign.

Solve;

Simplify by 4;
16/4=4
12/4=3

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