The wall thickness can be minimized by insulation layer

The wall thickness can be minimized by insulation layers. A typical wall having of a brick layer that has a thickness of d1 = 15 cm at the outside, a concrete layer with a thickness of d2 = 10 cm, an insulation layer (polystyrene foam) of thickness d3 and a gypsum layer with a thickness of d4 = 5 cm on the inside of the wall. Measure the thickness of the insulation layer and the total thickness of the wall to fulfil the needs of an energy-saving house.