Final answer:
The assertion and reason are both true, and the reason correctly explains the assertion. When two cubes of 6 cm sides are joined end to end, the surface area is indeed 360 cm², which is also confirmed by the formula provided in the reason.
Step-by-step explanation:
When two cubes each with a side of 6 cm are joined end to end, we need to calculate the surface area of the new solid. The assertion states that the surface area is 360 cm², while the reason gives a general formula for the surface area of n cubes each of side a units when joined end to end.
To verify the assertion, we must calculate the surface area of the two cubes joined together. Each cube has 6 faces, but when two are joined, one face from each cube will no longer be exposed. So we have (6 + 6 - 2) faces to account for, which gives us 10 faces total. The surface area of one face of a cube with a side of 6 cm is 6 cm × 6 cm = 36 cm². Therefore, the total surface area is 10 faces × 36 cm²/face = 360 cm², confirming that the assertion is true.
According to the reason, the surface area of two cubes joined end to end should be (4n + 2) × a². For two cubes, n=2 and a=6, we have (4×2 + 2) × 6² = (8 + 2) × 36 = 10 × 36 = 360 cm². This calculation also confirms the reason is true and coincides with the calculation we just performed for the assertion.
Both the assertion and reason are true, and importantly, the reason is the correct explanation for the assertion since the derived surface area from the reason matches the assertion's claimed value.