Easier than it looks, all you have to do is first subtract 13 from 299. You should get 286. Then, you just divide this number by two to get 143. Finally, since it asks for ZENA'S average, you add the 13 back to 143 to get the final answer of the average number of pins Zena took down, which is 156!
There is a formula for that; Total time = (Worker 1 * Worker 2) / (Worker 1 + Worker 2) Total time = (80 * 120) / (80 + 120) Total time = 9,600 / 200 Total time = 48 minutes
