Final answer:
To find the length of the line segment AC, the sin(40°) equation is used, with the result being approximately 12.9 units after calculations and rounding to the nearest tenth.
Step-by-step explanation:
The student's question seeks to find the length of the line segment AC using the equation sin(40°) = b/20. To solve for b, which represents the length of AC, we need to multiply both sides of the equation by 20. This yields b = 20 * sin(40°). Using a calculator, we find that sin(40°) is approximately 0.6428. Therefore, b = 20 * 0.6428 = 12.856. Rounding to the nearest tenth gives us that AC is approximately 12.9 units long.