The answer is 3 cm. You just have to add the sides you know (6 and 8) and subtract that from the perimeter (18)
The last one D because it is rational
So, you have 3/4x + 5/8 = 4x. We can do this in two ways. Since fractions are harder to deal with, we can turn the fractions into whole numbers.
First we need to find the LCD (Least Common Denominator) between 4 and 8, which is 8. So multiply the 3/4x by 2/2, which gives you an equivalent fraction of 6/8x.
So now we have 6/8x + 5/8 = 4x. Now multiply both sides by 8, to get rid of the denominators of the fractions. That gives us 6x + 5 = 32x. Now use the subtraction property of equality to subtract 6x from both sides giving us 5 = 26x.
Now you can use the division property of equality to divide 26 on both sides, which gives us x = 5/26.
Hope this helps. :D Feel free to ask any other questions, and if you have any questions about my explanation, don't hesitate to ask.
Answer:
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