We want to find the value that makes

To find it we must look at the standard normal table, using the complementary cumulative table we find that

Then, using the z-score we can find the minimum score needed, remember that

Where
σ = standard deviation
μ = mean
And in our example, x = minimum score needed, therefore

Rounding to the nearest integer the minimum score needed is 568, if you get 568 you are at the top 20.1%.
X will equal 4 because 4^2=4*4 which equals 16
She spent $23.25, how I got my answer.
I divided $13.50÷2=$6.75 then I added $6.75+3=$9.75 then I added $9.75+$13.50=$23.25.
I hope this helps.
1.choosing a red marble since the probability would be 7/12 but the blue would be 5/12 so red is most possible
2.the possibility of a red being chosen is 2/20=1/10