Mr. grant needs 30 pieces of felt.. he can but then in packs of 10 or as single pieces. what are the different ways mr. grant can buy the felt

Maximum number of packs of 10 = 30 / 10 = 3 packs

Therefore, the different ways to but them are as follows:
3 packs of 10 and zero single pieces (30-3(10)=0)
2 packs of 10 and 10 single pieces (30-2(10)=10)
1 pack of 10 and 20 single pieces (30-1(10)=20)
zero packs of 10 and 30 single pieces (30-0(10)=30)

Set square i think so

C