I need help please and thank you

Bradley hikes 12 miles in 3 hours. in relation to bradley’s hike, which statement describes the expression

Tod does not have any cookies. david gives jeff 8 cookies. then he splits half of the cookies he has left with tod. david let’s c represent the number of cookies that he starts with. he finds the number of cookies that tod has is 1/2 the difference of c and 8. write an expression to represent the number of cookies that tod has.

3x + 4y = 5 x- 3y = -7 solve by substitution