How do you beat the 3rd gym leader in emerald?

Location: Mauville City Pokemon Gym

Pokemon Type: Electric (some Steel)

Recommended Types: Ground, Fighting, Fire

Not Recommended Types: Water, Flying, Poison

Trainers:

Guitarist Kirk

Pokemon-

Lv. 18 Electrike

Lv. 18 Magnemite

Youngster Ben

Pokemon:

Lv. 19 Zigzagoon

Battle Girl Vivian

Pokemon:

Lv. 19 Meditite

Guitarist Shawn

Pokemon:

Lv. 17 Voltorb

Lv. 17 Voltorb

Lv. 17 Voltorb

Leader Wattson

Pokemon:

Magnemite Lv. 20

Voltorb Lv. 20

Magneton Lv. 22

Manectric Lv. 24

Difficulty: **

Prizes-

Third Badge: Dynamo Badge

TM Obtained: TM34- Shock Wave

HM Capability: Rock Smash

Money: 2300

If you want to defeat magneton get lvl 20 sableye found at crystal mine