I don't know how to get it properly but here's an alternative clue: the letter appears 23 times in this post (excluding the quoted part from you). Any clues for 30? I have four letters and have tried various combinations and alterations but can't find the right way.
Is that the equation one? If it is... Ignore the x10 bit because I don't think it fits that well All the left hand sides are 16 + 1 and all the right hand sides are 17. So you just have to figure out how to represent 17 for the last one. Someone help me with 26! I'm getting unsettled by having the same picture in front me me for so long.
I'm rubbish at clues But the answer to nine is nothing to do with what's written there.. (I'll PM you it if you want. If you help me with 13 when you get there.)