Plz help with physics 102...?

Question

The headlights on a car are rated at 80 W. If they are connected to a fully charged 90A h(hour) 12 V battery, how long does it take the batter to completely discharge?

Answer 1

energy consumption 80xtime

energy available

90x3600x12

equate both in  order to obtain

time=90x3600x12/80 seconds

Answer 2

Amps x Volts = Watts

Calculate current (amps) used by headlights:

80 W = Amps * 12V

Amps = 80 / 12 = 6.67 amps

Battery supplies 90 Ah = 90 amp-hr

Answer:

Headlights use 6.67 amps

Battery supplies 90 amp-hour

90 / 6.67 = 13.5 hours

The term, amp hour, was invented specifically to make this math easy.  Unfortunately, understanding what amp hour means is difficult.