What is the minimum amount of energy a plant
must absorb to produce 15.0 g of glucose?

The minimum amount of energy a plant  must absorb to produce 15.0 g of glucose is 57.0 kilo calories.

Explanation:

Energy released on combustion of 1 g gram of glucose = -3.80 kcal

Energy released on combustion of 1 grams of glucose = -3.80 kcal

So, the energy required to form 1 gram of glucose is = 3.80 kcal

The energy absorbed by the plants to produce 15 grams of glucose be :

The minimum amount of energy a plant  must absorb to produce 15.0 g of glucose is 57.0 kilo calories.