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Victon what I said !
To solve this, set up the equation, 90% of x being .9*x=57. Then, solve for x, x=57/.9=

=6.333
I don't have an idea about the 1st one but second one goes by subtracting 1/3
subtract 1/3 from 8 1/3 it's 8, subtract 1/4 from 8 it's 7 2/3. figuring out the patterns are simple most of the time bu you can get stuck sometimes, if you wanna get better, practice...