You will need to find the quadratic regression formula for this one on your calculator.
Go to STATS on your graphing calculator and select EDIT.
In the table, you will input all your x values in the first column, and all your y values in the second column correspondingly.
Be sure you table you clear before entering any data.
Go the STATS, and select CALC. From there, look for QUADREGRESSION. Select it.
Once you have your quadratic regression function, write it down on your paper.
Plug in y=6.2 into your regression formula and solve for x.
To solve for x, use the quadratic formula.