Expression equivalent to (-3x + 6.3y) - (-5x + 4.2y)

For each proportion find the unknown number x 1/5/8=×/15

Nick has box brads. he uses 4 brads for the first project. nick let’s b represent the original number of brads and finds that for the second project, the number of brads he uses is 8 more than half the difference of b and 4. write an expression to represent the number of brads he uses for the second project.

Math it's appreciated. (picture provided)