To find out how long it will take for the fish to reach a depth of -37.8 meters, we first need to figure out how far the fish needs to go from its original depth of -10.8 meters.
1. **Calculate the distance to descend:**
The fish starts at a depth of -10.8 meters and wants to get to -37.8 meters. We can find the distance it needs to descend by subtracting the two depths.
\[
-37.8 - (-10.8) = -37.8 + 10.8 = -27 \text{ meters}
\]
So, the fish needs to go down 27 meters.
2. **Calculate how many 1.5 meter descents are needed:**
Since the fish descends 1.5 meters every 2 minutes, we divide the total distance it needs to descend by the distance it goes down in each step.
\[
\text{Number of descents} = \frac{27 \text{ meters}}{1.5 \text{ meters/step}} = 18 \text{ steps}
\]
3. **Calculate the total time taken for the descents:**
Each descent takes 2 minutes, so we multiply the number of descents by the time per descent.
\[
\text{Total time} = 18 \text{ steps} \times 2 \text{ minutes/step} = 36 \text{ minutes}
\]
Therefore, it will take the fish **36 minutes** to reach a depth of -37.8 meters.
**Sentence Explanation:**
It will take the fish 36 minutes to swim down to -37.8 meters from its starting point of -10.8 meters.