Final answer:
To find the unknown value using a unit rate, divide the given ratio's numerator and denominator by the same value to get a unit rate of 5. Set up a proportion with the unit rate and the unknown value, cross-multiply, and solve for the unknown. The answer is 50.
Step-by-step explanation:
To find the unknown value, we can use the unit rate from the given equation. The unit rate is determined by dividing the numerator and denominator of one ratio by the same value to get a value of 1. In this case, we divide 75 by 15 to get a unit rate of 5. Then, we set up a proportion by writing the ratio 10/? as 10/1, since the unit rate is 5. Cross-multiplying, we find that the unknown value is 50. Therefore, the answer is A. 50.