Write a system of equations to describe the situation below, solve using substitution, and fill in the blanks.

Edwin is going to ship some gifts to family members, and he is considering two shipping companies. The first shipping company charges a fee of $11 to ship a medium box, plus an additional $6 per kilogram. A second shipping company charges $15 for the same size of box, plus an additional $4 per kilogram. At a certain weight, the two shipping methods will cost the same amount. What is that weight? How much will it cost?


At a weight of ___ kilograms, the two shipping methods both cost $___
.