At a model airplane​ show, Rosa can build 8 model airplanes in 3 hours. Zach can build 13 model airplanes in 5 hours.
a. Who builds model airplanes​ faster, Rosa or​ Zach?
b. How long will it take Rosa to build 20 model​ airplanes?
c. How long will it take Zach to build 20 model​ airplanes?