Answer:
n=14
Explanation:
These ratios can also be written this way:

cross multiply and you get:
7x18=9n
126=9n
n=14
The convection drive plates tectonics through a combination of pushing and spreading apart at mid-ocean ridges and pulling and sinking downward at subduction zones. At subduction zones, two tectonic plates meet and one slides beneath the other back into the mantle, the layer underneath the crust.
Gravel in the soil helps crops grow better, since they provide nutrients. Sand however, doesn't impact the crops growth at all.
Answer:
Countries trade with each other when, on their own, they do not have the resources, or capacity to satisfy their own needs and wants. By developing and exploiting their domestic scarce resources, countries can produce a surplus, and trade this for the resources they need.