Use a bar model: Ned = 1 unit, Billy = 2 units.

Billy + Ned = 3 units. Tom = 3 × 3 units = 9 units.

Ned = 1 unit	=
Billy = 2 units	=	Billy + Ned = 2 + 1 = 3 units
Tom = 3 × (Billy + Ned)	=	3 × 3 units = 9 units
Tom ÷ Ned	=	9 units ÷ 1 unit = 9