If i have a 73 grade average in high school what kind of grades would i need to bump it up to a 85?

You basically need grades above 95 to move your 73 average to 85.

There is no detail in your post to do a calculation, but here's a very oversimplified version of how weighted averages work:

Say your current 73 average (73%) represents 1 year of work (let's say 45 credits). If you average 97% next year (worth another 45 credits), your new overall average would be

{ [(0.73 x 45) + (0.97 x 45)] / 90 } = 0.85 = 85%

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If your current average represents 2 years of work, it will take longer to raise your overall average. The 'weight' of the 73% average would be greater, making it slower for the overall average to change even if you get high grades.

I'll show you what I mean. Continuing the above example, say that your average is 73% after 2 years (90 credits). In your 3rd year (45 credits), you get a 97% for the year. Your new overall average would be

{ [(0.73 x 90) + (0.97 x 45)] / 135 } = 0.81 = 81%

I'm basically just talking about the concept of weighted averages. It's not just the grades that count; it's also the number of credits taken.