Someone help me please .

This element has 8 protons, so element is oxygen. I recommend looking at the periodic table of elements. At standard temperature and pressure (STP), oxygen is a gas, so that puts it in the nonmetal category.

Side note: Metalloids are a collection of elements where they share properties of metals and nonmetals (in a way they're on the fence).

6 adults and 9 children went.

a + c = 15

12a + 9c = 153

12(6) + 9(9) = 153

72 + 81 = 153