Think of PEMDAS, or Please Excuse My Dear Aunt Sally. Which is Parentheses, Exponents, Multiplication and Division, and Addition and Subtraction in that order.
Hi,
Perimeter AEDCB=3*10+15+20=65 (units)
Ratio of the similitude r*15=21==>r=21/15=1.4
Perimeter RQPTS=65*1.4=91(units)
More members prefer a beach vacation and a ski vacation than a cruise vacation