Nur Rechnen - Maths only

a:??0??0??0??= 6
b:??1??1??1??= 6
c:??2??2??2??= 6
d:??3??3??3??= 6
e:??4??4??4??= 6
f:??5??5??5??= 6
g:??6??6??6??= 6
h:??7??7??7??= 6
i:??8??8??8??= 6
k:??9??9??9??= 6