Answer:
7 hours
Explanation:
The total charge contained in the battery is
[tex]Q = 49 A \cdot h[/tex]
And this is a charge, since it is a current multiplied by a time:
[tex]Q=It[/tex]
The current drawn by each headlight (which is the charge consumed per second) is
[tex]I=3.5 A[/tex]
Since we have two headlight, the total current drawn is
[tex]I=3.5 \cdot 2 = 7 A[/tex]
Therefore, the total charge consumed by the two headlights each hour is
[tex]q = I \cdot h = 7 A \cdot h[/tex]
So, the time before the battery is dead is
[tex]t=\frac{Q}{q}=\frac{49 Ah}{7Ah}=7 h[/tex]
