The length of a backpack of capacity 30 liters is 53 cm.

Calculate the length of a mathematically similar backpack of capacity 20 liters.

Can someone explain to me this problem and how to solve it?

Work out how many cm per litre

53cm / 30 liters = 1.77cm/L, then multiply by the litres to work out length

20 liters x 1.77 cm/L = 35.4cm

Therefore, the length of the backpack with capacity of 20 liters is 35.4cm.