$\quad i \, \heartsuit \text{ Brilliant}$

$ab=10a+b$ $\color{#D61F06}{......(1)}$

$ba=10b+a$ $\color{#D61F06}{......(2)}$

Subtracting $\color{#D61F06}{(2)}$ from $\color{#D61F06}{(1)}$ ,

$ab-ba=9(a-b)$ which is divisible by 9.

So by divisibility test of 9, $\boxed{c=5}$ as 5+4=9|9

We should first notice that $ab = 10a + b$ and $ba = 10b+a$ and $c4 = 10c +4$ ...

$10a + b - 10b - a = 10c +4$

$9a - 9b = 10c + 4$

Since the remainder of 4 for any multiple of 10 has a ones digit of 4, we need to find a two-digit multiple of 9 which ends in a 4. Thus we realize that $9 * 6 = 54$ . And therefore...

$10c + 4 = 54$

$10c = 50$

$c = \boxed{5}$

82-28=54.. Hence u can see i've simple figured it out by guessing..