Can you all help me out? The proportions just keep tripping me up :(

What is the rotational symmetry of a wheel

Determine which expressions represent real numbers and which expressions represent complex number. asaaap! plis!

Suppose you are choosing a 6-digit personal access code. this code is made up of 4 digits chosen from 1 to 9, followed by 2 letters chosen from a to z. any of these digits or letters can be repeated. find the total number of personal access codes that can be formed. 492,804 341,172 39,917,124 4,435,236