Let's solve the problem step by step:

1. Round each measurement to the nearest ten:

   • Length: $42$ inches rounds to $40$ inches.
   • Width: $86$ inches rounds to $90$ inches.

2. Estimate the area of the rectangle:

   • The area $A$ of a rectangle is calculated by multiplying the length and width. $A = \text{length} \times \text{width} = 40 \times 90 = 3600 \, \text{square inches}.$

Therefore, the estimated area is 3,600 square inches, which matches the second option.

Would you like more details or have any questions?

Here are 5 related questions to expand on this:

1. What would the exact area be without rounding the measurements?
2. How does rounding affect the precision of your answer?
3. What is the perimeter of the original rectangle?
4. If you changed the units to feet, what would the dimensions and area be?
5. What is the formula for finding the area of other shapes, such as triangles or circles?

Tip: When estimating, rounding to the nearest ten or hundred can simplify complex calculations while maintaining reasonable accuracy.