need to find MAX value IF meets criteria

hello i need to find the maximum value for each letter from an array which will be mixed up like below. the array and number of unique letters will be alot more!

a 1 = should =7
b 2 = should = 8
c 3 = should = 9
a 4 = should =7
b 5 = should = 8
c 6 = should = 9
a 7 = should =7
b 8 = should = 8
c 9 = should = 9