Abiker decided each biker will carry a backpack the same fraction of weight. so hiker weight 152 lb 4 oz. how much will the backpack weight.

Unfortunately, you have not provided all of the necessary info to solve this problem.  So I have to make some assumptions.  Assume that the 152 lb 4 oz biker can carry a 22 lb backpack.  What fraction of 152 lb 4 oz is 22 lb?

Form the ratio             22 lb
                                =   ?
                                 152 lb 4 oz

Convert 152 lb 4 oz to lb:  152 lb 4 oz = 152.25 lb

Then

Form the ratio             22 lb               22 lb            88
                                = =                                                                      152 lb 4 oz       152.25 lb       609

Now, each biker may / can / must carry a backpack weighing (88/609) times his or her own weight.

I weigh 251 lb.  Therefore, I must carry a backpack weighing (88/609)(251 lb), or 36.27 lb.