Chapter 1 - Introduction to Algebraic Expressions - 1.1 Introduction to Algebra - 1.1 Exercise Set - Page 8: 28

(a) 90 sec (b) 270 sec (c) 6 min

Justin's time is 3t. (a) If t is 30 sec the time it takes Justin is: $3(30\ sec)=90\ sec$ (b) If t is 90 sec the time it takes Justin is: $3(90\ sec)=270\ sec$ (c) If t is 2 min the time it takes Justin is: $3(2\ min)=6\ min$