Given $\frac{x}{y}=\frac{10}{4}.$ If $y = 18$, what is the value of $x$?
I need to find $x$, and I have a proportion that relates $x$ and $y$. I can use cross-multiplication to solve for $x$: $x \times 4 = y \times 10$. Plugging in $y = 18$, I get $x \times 4 = 18 \times 10$. Simplifying, I get $x \times 4 = 180$. Dividing both sides by 4, I get $x = \frac{180}{4}$. I can simplify this fraction by dividing both the numerator and the denominator by 4: $x = \frac{180}{4} = \frac{45}{1} = 45$. 