Answer
A student must get a raw score of $49$ to get a passing adjusted grade.
Work Step by Step
Since a passing grade is a $70$, we would substitute $70$ in for $A$ to get the equation
$70=10\sqrt R$.
Then we would divide both sides by $10$ to isolate the variable; this would give the equation
$7=\sqrt R$.
Finally, we would square both sides to eliminate the square root being performed on R; this would give the equation
$49=R.$
Therefore, a student must achieve a raw grade of $49$ to get an adjusted grade of $7$0, which is the lowest possible passing grade.
