There's an app called photomath that would be useful for these kinds of problems!
Answer:
10.1 cm
Step-by-step explanation:
1.2 + 0.8 + 2.4 + 1.9 + 1.5 + 2.3 = 10.1 cm
The answer would be 13.9 kg of gravel used per square meter
Your question's correct answer would be -5. Hope this helped!