Verify clairaut's theorem for u=e^xysiny

The equation respenting the left table is

Tcan be concluded that % of the seniors would prefer to see more candid pictures in this year's edition of the yearbook.

The u-drive rent-a-truck company plans to spend $13 million on 320 new vehicles. each commercial van will cost $25 comma 000, each small truck $50 comma 000, and each large truck  $80 comma 000. past experience shows that they need twice as many vans as small trucks. how many of each type of vehicle can they buy?