Answer
(a) 2.5 feet
(b) 180 years old
Work Step by Step
We use unit conversions to solve the problem. To do this, we multiply by different fractions until every unit except the final unit we want is cancelled out. Doing this, we find:
(a)
$$ = 30 \ inches \times \frac{ft}{12\ inches} \\ = 2.5 \ feet$$
(b) The old tree grew at the following rate:
$$ =\frac{380 \ feet}{700 years} \\ = .54 \frac{feet}{year}$$
The young tree needs to grow 100-2.5=97.5 feet more. The time this will take is:
$$ =\frac{97.5 \ ft}{\frac{.54\ ft}{year}} \\ = 180 \ years$$
