1)how long...Paul? a)do you know b)have you known c)has you known

1) How long have you known Paul? We use the verb in the Present Perfect because the period if action includes also the present moment. 

2) Our teacher wears big brown glasses. We use the adjectives in the fixed order according to the general rule: size, color, etc. 

3) How did you get there? - On foot. We say by bus  by car, by train but on foot .