Airliners rule is to add 1/2 the headwind plus all the gust (above the headwind) up to max 20kts.
so in your example (app70 kts Hwind 18 kt G30) add 1/2 of 18 kts plus 20 kts for gust = 29 kts. Approach speed is therefore 98 kts.
I know this will meet with some controversey and it does seem too fast.
However lets analyse what we are doing. First the gust- it means exactly that. One minute its there, the next its gone - very dangerous. If one only adds 1/2 gust then next minute one will have minus 1/2 gust - not safe.
The headwind correction partly restores the ground speed so no risk of running out of runway.
This is for Approach say 4 mls Dme to near threshold. Nearing threshold start to reduce power and round.
In practise for a Piper, I would certainly add the gust correction and maybe ease up on the headwind and use 1 or 2 stage flap subject to runway.
I would question the wisdom of flying a light aircraft on a day with G30 knots at the airport - that is a lot of wind, particularly as you are a student. I don't think I would get airborne.
flyme