Van traveling at 30 km/h slows to 20 km/h in 3 seconds. what is the acceleration of the van?

i know the formula end velocity- starting velocity divided by time. my question is do you to convert km/h to m/sec?

The temperature in gavin's oven is a sinusoidal function of time. gavin sets his oven so that it has a maximum temperature of 280°f and a minimum temperature of 240°. once the temperature hits 280°, it takes 20 minutes before it is 280° again. gavin's cake needs to be in the oven for 30 minutes at temperatures at or above 270°. he puts the cake into the oven when it is at 260° and rising. how long will gavin need to leave the cake in the oven? (round your answer to the nearest minute.)