If I have a 91 in reading and got a 55 on a Test what will my grade be now?

It depends.

What is the weighted average of everything?

Test make up what % of your grade, and was it 55/100? what is the total value of the cumulative tests 555/1230?

The test is 20% of my grade. And yes it is 55/100.

This one test accounts for 20% of your overall grade?

So then, 91% is based on 80% of your mark.

so x/80=.91
x = 72.8/80
+ 55% of 20 = 11/20

based on these calculations, your new grade is 83.8/100 = 83.8%

However, I suspect that all tests make up 20% of your grade, in which case, you need to know the results of all tests to determine the grade.