11. The Martins' oil furnace can produce 125,000 Btu's of heat in an hour when it is
3.5 hours?

437500  Btu's of heat is produced in 3.5 hours.

Explanation:

Given that,

The Martins' oil furnace can produce 125,000 Btu's of heat in an hour.

We need to find heat produced in 3.5 hours.

1 hour = 125,000 Btu's of heat

For 3.5 hours,

3.5 hour = 3.5 × 125,000 Btu's of heat

= 437500  Btu's of heat

So, 437500  Btu's of heat is produced in 3.5 hours.