The following function f is one-to-one; find its domain and range.

f(x) = 5 / x+3

Domain = x cannot be -3
Range= I do not know how to find this.

consider it as

y = 5/(x+3)

Can you replace any number for y ?
let's try y = 8
8 = 5/(x+3)
8x + 24 = 5
etc.
notice we could put any number for y and we would get a solution for x, or ....
what about y = 0
0 = 5/(x+3)
0(x+3) = 5
0 = 5 -----> contradiction

so y can be anything except y ≠ 0
there is your range.