fix(challenge-md): Fix file names and preserve challenge order in meta.json

curriculum/challenges/en/08-coding-interview-prep/project-euler/problem-72-counting-fractions.en.md

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+---
+id: 5900f3b41000cf542c50fec7
+challengeType: 5
+title: 'Problem 72: Counting fractions'
+---
+
+## Description
+<section id='description'>
+Consider the fraction, n/d, where n and d are positive integers. If n<d and HCF(n,d)=1, it is called a reduced proper fraction.
+If we list the set of reduced proper fractions for d ≤ 8 in ascending order of size, we get:
+1/8, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 1/2, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 7/8
+It can be seen that there are 21 elements in this set.
+How many elements would be contained in the set of reduced proper fractions for d ≤ 1,000,000?
+</section>
+
+## Instructions
+<section id='instructions'>
+
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+- text: <code>euler72()</code> should return 303963552391.
+  testString: 'assert.strictEqual(euler72(), 303963552391, ''<code>euler72()</code> should return 303963552391.'');'
+
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function euler72() {
+  // Good luck!
+  return true;
+}
+
+euler72();
+```
+
+</div>
+
+
+
+</section>
+
+## Solution
+<section id='solution'>
+
+```js
+// solution required
+```
+</section>