Shown below is a keyboard designed for smartphones. It has two sizes of keys which are arranged one after the other. What will be the difficulty of independently typing a single coloured key from the origin (key O), arranged from least difficult to most difficult i.e. easiest to type first, most difficult to type last. Assume, the mobile is held vertically in the left hand, and a right-handed user presses the keys using only the index finger of the right hand. [Figure: see page 12 of source PDF]