To solve this problem, we'll use the formula for direct variation:

$y = kx$

where $k$ is the constant of variation.

Step 1: Find $k$

We are given that $y = 90.3$ when $x = 7$. Using this information, we can substitute these values into the equation to solve for $k$.

$90.3 = k \cdot 7$

Now, solve for $k$:

$k = \frac{90.3}{7} = 12.9$

Step 2: Use $k$ to find $y$ when $x = 3.6$

Now that we know $k = 12.9$, we can substitute this into the direct variation equation to find $y$ when $x = 3.6$.

$y = 12.9 \cdot 3.6$

$y = 46.44$

Final Answer:

When $x = 3.6$, $y = 46.44$.

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Would you like further explanation or have any questions? Here are some additional questions you might find interesting:

1. What happens to the value of $y$ if $x$ is doubled?
2. How does the constant $k$ affect the rate of change between $x$ and $y$?
3. Can the direct variation equation be used if $y$ varies inversely with $x$?
4. How would the equation change if $y = 5x + 10$ instead of $y = kx$?
5. What is the relationship between direct variation and proportionality?

Tip: Always remember that in direct variation, the ratio $\frac{y}{x}$ remains constant.