Hints:
Let $x$ be the length purchased from the wholesaler
Price per meter paid to wholesaler: $p_w = \dfrac{1120}{x}$
Price charged to customer per meter: $p_c =\dfrac{1600}{x+4}$
Stated inequality: $p_c \ge p_w+10$
Substitute and solve the quadratic inequality to get a range for $x$. For example $x=2$ and $x=200$ do not work, but $x=20$ does work