What is the unit rate 3 for $5 4 for$6

You have two separate problems here.  

a) 3 for $5 needs to be expressed as cost per unit.  Write $5/(3 units), and then simplify.  Here the unit rate is ($5/3) / unit, or $1.67 per unit.

b)  4 for $6:  Write $6/(4 units), and then reduce to lowest terms:  
(6/4) dollars per unit, or $1.50/unit

Claude debussy's music was associated with answer choice 3, impressionist