Trying to create an IF function with an AND statement

Hello,

I am trying to write an IF function that will add 10 extra points to a grade if extra points are available and the points earned are greater than zero.

Here's an image of my current spreadsheet



So what I am trying to do with this IF function is, if the number in B23 is greater than zero, add whatever that number is to B20, and have the answer populate in B24 as a percent. If possible also populate the corresponding letter grade into B25. If this part is not possible I can always use VLOOKUP for B25 to figure out the corresponding grade based on the new percentage in B24.

Thank you!

can you attach a sample spreadsheet rather than a image saves typing all the data in ourselves

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for B24 ,
=IF(B23>0,(SUM(PointsEarned)+B23)/SUM(PointsPossible),"")
for b25
=IF(B23>0, VLOOKUP(B24,GradingScale,2,TRUE),"")