Final answer:
The correct answer is option A, $85.67, for the total cost of mercury used to make 21 manometers by calculating the volume, then the weight, and finally the cost of mercury at $1.99 per pound.
Step-by-step explanation:
The correct answer is option A, $85.67. First, we need to calculate the volume of mercury needed for 21 manometers. Since one manometer takes 2.050 in3 of mercury, for 21 manometers we multiply 2.050 in3 by 21, which equals 43.050 in3.
Next, to find out how much this volume weighs, we use the density of mercury which is about 0.490 pounds/in3 (since 13.6 grams/cm3 is equal to 0.490 pounds/in3, given that mercury is 13.6 times denser than water). By multiplying the total volume by the density, we get the weight in pounds: 43.050 in3 times 0.490 pounds/in3 equals approximately 21.10 pounds. Finally, multiply the weight of the mercury by the cost per pound, $1.99 per pound, to find the total cost: 21.10 pounds times $1.99/pound equals approximately $41.97 for the mercury needed for one manometer.