2+2 answer please help me

Which of the following is most likely the next step in the series? a3z, b6y, c9x, d12w, е15v, f18u

Ineed me i stuck and i don’t want to get it wrong

40 points. given: two congruent angles ∠c and ∠r are supplementary. prove: ∠r and ∠c are both right angles. it doesn't have to be exactly 10 rows.statements reasons1. 1. 2. 2. 3. 3. 4. 4. 5. 5. 6. 6. 7. 7. 8. 8. 9. 9. 10. 10.