At Johnmiedema.ca, we help you find the right answers. Let's share knowledge and experiences together.

## Sagot :

1.

**Understand the problem:**

- The boat travels downstream with the current.

- Distance traveled downstream: 9 miles.

- Time taken for the downstream journey: 90 minutes (which is 1.5 hours).

2.

**Define variables:**

- Let [tex]\( x \)[/tex] be the speed of the boat in still water (miles per hour).

- Let [tex]\( y \)[/tex] be the speed of the current (miles per hour).

3.

**Determine the effective speed:**

- When the boat is traveling downstream, its effective speed is [tex]\( (x + y) \)[/tex] because the current aids the boat.

4.

**Use the distance formula:**

- The formula for distance [tex]\( d = r \cdot t \)[/tex], where [tex]\( r \)[/tex] is the rate (or speed) and [tex]\( t \)[/tex] is the time.

- Given [tex]\( d = 9 \)[/tex] miles and [tex]\( t = 1.5 \)[/tex] hours, we can set up the equation for downstream travel:

[tex]\[ 9 = 1.5 \cdot (x + y) \][/tex]

5.

**Formulate the equation:**

- Rearrange the equation to solve for [tex]\( (x + y) \)[/tex]:

[tex]\[ x + y = \frac{9}{1.5} \][/tex]

[tex]\[ x + y = 6 \][/tex]

- However, since we are comparing to options provided:

- The correct equation directly relating distance, speed, and time is:

[tex]\[ 9 = 1.5 \cdot (x + y) \][/tex]

From the given multiple-choice options, the correct one that matches our derived equation is:

[tex]\[ 9 = 1.5(x + y) \][/tex]

Hence, the correct answer is:

[tex]\[ 9 = 1.5(x + y) \][/tex]