How long does the Brazilian hair straightening treatment last?

The treatment I use for Brazilian straightening is absolutely safe and lasts about four months, depending on the individual hair type. After this treatment you will find that you can more easily and much more quickly manage your own hair. This treatment leaves practically all hair types very silky and naturally shiny.
Depending on your hair's length, the treatment takes something in the region of 1½-2 hours. The treatment I use is keratin based which is of proven benefits to all hair types. Depending on hair length and type, the price range for the full treatment (washing, product application and drying - all with dedicated quality products) is £70-90.

my hair lenth shoulder so how many kit use and price please

how long time straight and I do my self

A brazilian straightening treatment should last about 10 to 12 weeks. Generally, the worse the state the hair, the more benefit a treatment will bring as it is essentially a repairing treatment.
Also, to get the most from a straightening, it's best to avoid shampoos that contain salt (sodium chloride) as this shortens the life of a treatment.
Hope this helps,