Answer:
A trainee requires 3 days of training before they can assemble 9 heaters.
Explanation:
We are given the formula for the number of water heaters h that a trainee can assemble per 8-hour shift as:
h = 2.1 0.9t + 4
where t is the number of days of training the trainee has received. We need to find out how many training days are required before a trainee can assemble 9 heaters. So we set h to 9 and solve for t:
9 = 2.1 0.9t + 4
Subtracting 4 from both sides, we get:
5 = 2.1 0.9t
Dividing both sides by 2.1 0.9, we get:
t = (5 / (2.1 0.9))
Using a calculator, we get:
t ≈ 2.49
Rounding up to the nearest day, we get:
t = 3
Therefore, a trainee requires 3 days of training before they can assemble 9 heaters.