Knowing that x varies directly with y, we know the basic skeleton of the equation is y = mx.
To find m, plug in the known coordinate (8,10), where the x-coordinate is 8 and the y-coordinate is 10.
[tex]y=mx \\ 10=m8 \\ (10)/8=(8m)/8 \\ m= \frac{10}{8} = \frac{5}{4} [/tex]
Then, plug in m to the equation to get y = (5/4)x.
Finally, plug in the y-coordinate 18 to the equation and solve for x!
[tex]y= \frac{5}{4}x \\ 18= \frac{5}{4}x \\ \frac{4}{5}(18)=( \frac{5}{4}x) \frac{4}{5} \\ x= \frac{4*18}{5} \\ x= \frac{72}{5} [/tex]
Your exact answer is x = 72/5. However, if your teacher prefers decimals, then x = 14.4
Hope this helps!
