The brother is represented by variable b.
The sister is represented by the variable s.
This means:
b+s=26
The answer is 14.22 mg / (mm^2)
The best answer is:
a. Extrusive igneous rocks
In general, rocks that are formed by the cooling of magma are classified as igneous rocks. The key word however in this case is "lava," which is magma that reached the surface. This is what makes it an extrusive igneous rock, because it formed in the surface.
