My car's steering wheel shakes when I go over 75 miles.?

Update: My car's steering wheel shakes when I go over 75 miles I took it to Les Schwab and they balance the tires. That made no difference. So I went back and they put other used tires but it still does the same any ides what can it be ?
Update 2: Car only have 98 thousand miles on it I checked and tie rofs are good. Nothing seems to be worn out or broken.
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