Explanation:
Igneous rocks are formed by melting and cooling of magma originated from volcanic process.
when molten rock (rock liquefied by intense heat and pressure) cools to a solid state. Lava is molten rock flowing out of fissures or vents at volcanic centres (when cooled they form rocks such as basalt, rhyolite, or obsidian)
These rocks are strong, crystalline and dark in colour.
I believe the answer is b. external stimulus
After the second car starts out,
D = 30 + 110 H
360 = 30 + 110 H
330 = 110 H
H = 330/110
H = 3 hours after the second car leaves.
That's 3.5 hours after the first car leaves.
The ID, or Independent Variable, I think.