The national grid supplied a house with 18000000 J of energy in 1 hour. What was the average current supplied to the house in that hour? Write any equations that you use.

Electrical power = (voltage) x (current)

Electrical energy = (power) x (time)

Combine those definitions:

Energy = (voltage) x (current) x (time)

Divide each side by (voltage x time), and we have

Current = Energy / (voltage x time)

You told us that

Energy = 1.8 x 10⁷ joules

Time = 1 hour = 3,600 seconds

so we have

Current = (1.8 x 10⁷) / (voltage x 3,600).

If you live in the US, Canada, or Mexico, your voltage is 120 volts.

Current = (1.8 x 10⁷) / (120 x 3,600) = 41-2/3 Amperes

If you live practically anywhere else in the world, your voltage is 240 volts.

Current = (1.8 x 10⁷) / (240 x 3,600) = 20-5/6 Amperes.