Evaluate the expression for 3x plus 12 plus 7x plus x

What is the missing step in this proof? scroll down to see the entire proof. u

In the image, layer a is the topmost layer. layer c contains fossils from the precambrian era. layer b contains dinosaur fossils, and layer a contains fossils of mammals. which two statements are supported by this evidence? 1. mammals lived before the precambrian era. 2. dinosaurs and mammals existed in the precambrian era. 3. dinosaurs evolved after precambrian organisms. 4. precambrian organisms evolved after dinosaurs. 5. precambrian organisms were the first life-forms to become fossilized, according to this sample.

What are the three stages of volcanic activity? a. active, magma, lava c. extinct, eruption, explosive b. eruption, quiet, explosive d. active, dormant, extinct