Yes. You can find the third inside angle by adding the other two together and subtracting it from 180(degrees). This is because the inside of a triangle will always be 180. You can find the missing sides by using the law of sines. (SinA/a = SinB/b = SinC/c)
180 - (45+30) = 105
Sin(45)/18 = Sin(30)/x
x = (18sin(30))/sin(45) = 12.7279220614…
Sin(45)/18 = Sin(105)/x
x = (18sin(105))/sin(45) = 24.5884572681…