Jan has 39 pieces of Lego in a box. Frank has 12 more pieces of Lego than Jan in another box. How many pieces of Lego do they have together?

pieces of Lego

The number of pieces of Lego for Frank : 39 + 12 = 51

The sum of pieces of Lego: 51 + 39 = 90

They have 90 pieces of Lego together.