The cost for an electrician is $135 for 3 hours. A 7 hour repair costs $315. Showing your calculations, determine the price of a 12 hour repair.

135/3 = 315/7 = 45 per hour

45 * 12 = $ 540

To determine the price of a 12 hour repair, we need to find the cost per hour for the electrician's services.

First, let's find the cost per hour for the 3-hour repair using the given information that it costs $135. We can set up a proportion:

(3 hours) / ($135) = (1 hour) / (x)

Cross-multiplying, we have:

3x = 135

Dividing both sides by 3:

x = 45

So the cost per hour for the electrician's services is $45.

Next, let's find the cost per hour for the 7-hour repair using the given information that it costs $315. We can set up another proportion:

(7 hours) / ($315) = (1 hour) / (x)

Cross-multiplying, we have:

7x = 315

Dividing both sides by 7:

x = 45

Again, we find that the cost per hour for the electrician's services is $45.

Now, to find the price of a 12-hour repair, we can use the cost per hour of $45:

Price of 12-hour repair = (12 hours) × ($45/hour)
Price of 12-hour repair = $540

Therefore, the price of a 12-hour repair is $540.