Nav. Computer:  Put 100 (sm) next to stat.m. index and read distance next to naut.m. index: 86.5nm.  

Put 20 (minutes) on inner scale next to 86.5 (nm) on outer scale; groundspeed 260 kts (on outer scale next to 60 on inner scale). 

Go to 215 (nm) on outer scale and read time in minutes on inner scale: 49.5 minutes.

Calculator: 100x5280÷6080 = 86.84 nm÷20x60 = 260.5 kts, 215÷260.5 = 0.825 hr, 0.825x60 = 49.52 minutes.