**Option C; After draining for 40 hours, both tanks will have 54 gallons of water remaining.**

**Step-by-step explanation:**

**Step 1;** First we are required to find the rate at which tank A is losing water. The first tank after draining for 8 hours has 70 gallons remaining inside and in 20 hours contains 64 gallons. So in 12 hours (20 hours - 8 hours) tank A has lost 6 gallons. So tank A is losing 6 gallons in 12 hours which translates to tank A losing 0.5 gallons every hour.

**Step 2;** Secondly we find the rate at which tank B is losing water. The second tank after draining for 10 hours has 60 gallons and in 30 hours contains 56 gallons of water. So in 20 hours (30 hours - 10 hours) tank B has lost 4 gallons. So tank B is losing 4 gallons in 20 hours which translates to tank B losing 0.2 gallons every hour.

**Step 3;** Now we calculate how much water would be in the tanks after the different periods of time.

So for tank A at a rate of water draining 0.5 gallons per hour, there would be

54 gallons remaining in 40 hours, 50.5 gallons remaining in 47 hours, 47 gallons remaining in 54 hours and 40 gallons remaining in 68 hours.

For tank B at a rate of water draining 0.2 gallons per hour, there would be

54 gallons remaining in 40 hours, 52.6 gallons remaining in 47 hours, 51.2 gallons remaining in 54 hours and 48.4 gallons remaining in 68 hours.

So in 40 hours, both tank A and B will have 54 gallons of water in them. So option C is the answer.