Memorize the nombers. You can do it! So, you ask, how do I know that M is 3 and P is 9? The answer is that you must first memorize the following table of consonants and digits. Oh dear, you say. But wait... once this chart is memorized, it can be used for life! And second, there's even a scheme to associate the numbers with the letters!
NUMBER LETTER/SOUND MEMORY AID
1 t, d t has one down stroke
2 n n has two down strokes
3 m m has three down strokes
4 r "four" ends with R
5 l Latin 50 = L
6 j, sh, ch J reversed looks like 6
7 k, g (hard) Visualize a K drawn with two 7s
8 f, v Cursive f has two loops like an 8
9 p, b P reversed looks like 9
0 z, s "zero" starts with Z