Asculptor bought 15 blocks of wood for a total of $139.50.the 3 large blocks cost a total of $25.50 the remaining small blocks each cost the same amount. how much did each small block cost explain your answer plz

We have 15 block there is 3 large blocks which leave 12 small ones 
the total price of all is 139.50 if we subtract the price of the 3 large ones 139.50-25.50=114$ we will have the price of the 12 small blocks left (114$)
to know the price of 1 small block we must divide the total price by the number of the small blocks (that is 12 block) 114÷12=9.50$ 
the price of 1 small block is 9.50$