So, assume she starts at 0. Then, subtract 18, sense she lost 18 points.
She now has -18 points. Part 2, she gained 22, so its -18 + 22, which is 4.
She now has 4 points. Part 3, she gained 4 points, so its 4 + 4, which is 8.
Marta's score on the endurance test is 8.
Hope this helps!!!
~Kiwi