If required rate of return is 12% and per unit cost of units purchased is $35, then relevant opportunity cost of capital will be

The correct answer is A. $6.20.

The opportunity cost of capital is the return that could be earned on an alternative investment with the same risk. In this case, the required rate of return is 12%, so the opportunity cost of capital is $6.20 per unit. This is because if the company invests $35 in a new project, it will forgo the opportunity to earn $6.20 in interest on that money.

Option B is incorrect because it is the cost of the units purchased, not the opportunity cost of capital. Option C is incorrect because it is the difference between the required rate of return and the cost of the units purchased. Option D is incorrect because it is the cost of the units purchased plus the opportunity cost of capital.