heres my equation: c(coat)+s(shirt)+t(tie)=$300 c=2s s=2t+40

i need to know how to solve this to get the cost of each item?

just substitute the various quantities:

c+s+t=300
2s+s+t=300
3s+t = 300
3(2t+40)+t = 300
6t+120+t = 300
7t + 120 = 300
7t = 180
odd that you don't get an exact divisor.
Oh well, get t and then you can get c and s.