Sara Bredbenner and Blake DeYoung are teammates at a discount store; their new job is assembling swing sets for customers. Assembly of a swing set has a learning rate of 90%. They forgot to time their effort on the first swing set, but spent 4 hours on the second set. They have 6 more sets to do. Determine approximately how much time will be (was required for:
(a) The 1st unit
(b) The 8th unit
(c) All 8 units.