Answer: He should plant 48 tulips.
Lets start by using the ratio 6:1 to represent that for every 6 tulips there are 1 rose.
Simply keep adding 6 to the left side of the ratio and 1 to the right side until the total of the ratio is 56 flowers.
6:1 6 + 1 = 7
12:2 12 + 2 = 14
18:3 18 + 3 = 21
24:4 24+4=28
30:5 35 + 5 = 40
36:6 36+6=42
42:7 42 + 7 = 49
48:8 48 + 8 = 56 total flowers
So, he should plant 48 tulips.