Question 444783
f(x) = 5x + 21/x ; f(x) = -38
..
-38 = 5x + 21/x 
multiply by x
-38x=5x^2+21
5x^2+38x+21=0
solve by quadratic formula
a=5, b=38, c=21
x=[-38+-sqrt(38^2-4*5*21)]/2*5
x=[-38+-sqrt(1024)]/10
x=(-38+-32)/10
x=-70/10=-7
or 
x=-6/10=-.6