Six identical rectangular boxes can be stacked into a cupboard 90 cm wide. Two arrangements are shown below. The first arrangement in Figure A leaves a 42-cm gap at the top. The second one in Figure B leaves a 10-cm gap at the top and another gap at the side.
(a) In the arrangement shown in Figure B, what is the width of the gap at the side?
(b) What is the height of the cupboard?