Marie has a small copy of Rene Magritte's famous painting, The Schoolmaster. Her copy has dimensions 2 inches by 1.5 inches. The scale of the copy is 1 in.:40 cm

A scale of 1:40 can be read as "one cm on the model corresponds to 40 cm in the original object". or

"one inch on the model corresponds to 40 inches

this means that the 2 inches correspond to 2 times 40, that is 80 inches and 1.5 corresponds to 1.5*40=60 inches

which means that the original paintong has dimentions of 80 by 60 inches.