Hi, i'm working through the aqa pure core maths book 1, just started, am looking at a wordy-type question. here it is

'a rectangular plot of land has dimensions 2x + 3 metres by 5x - 4metres. Explain why x > 4/5.

Given that the perimeter is less than 40metres, find another inequality satisfied by x'

with some trial and error i saw that with x less than or equal to 4/5, you get a negative number, or 0, which i knew couldn't be a correct dimension. didn't work it out mathamatically i guess, but still understood it basically. its the second part i can't get.

here's the answer in the back of the book.

"5x-4 > 0 (can't have a negative length), therefore 5x > 4, therefore x > 4/5. Then, x < 3"

i think the 'x < 3' is refering to the second part of the question, but i don't understand how they got 3. please help!

Use the formula for the perimeter of a rectangle. Substitute your expressions, and you will see how x < 3.

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but of course! bah!

thanks very much!