15% of body weight help.

Find 10% (10% of 407 is 40.7, so you can use 40 to make it easier). Then take half of that amount (20) and add it to the 10% (40 + 20 = 60)

120 grams:
120 x .10 = 12
12/2 = 6
12 + 6 = 18