How many 7-digit telephone numbers can be formed if the first digit cannot be 0 or 1

An air conditioning system can circulate 350 cubic feet of air per minute. how many cubic yards of air can it circulate per minute?

Any is very appreciated! (picture is provided below)not sure how to do this at all won't lie

1. 2. ∠b and ∠y are right angles. 3.? 4.? which two statements are missing in steps 3 and 4? ∠x ≅ ∠c △abc ~ △zyx by the sas similarity theorem. ∠b ≅ ∠y △abc ~ △zyx by the sas similarity theorem. = 2 △abc ~ △zyx by the sss similarity theorem. = 2 △abc ~ △zyx by the sss similarity theorem.