The graph of $y=f(x)$ is shown below, with $1$ unit between grid lines. Assume $f(x)$ is defined only on the domain shown. What is the sum of all integers $c$ for which the equation $f(x)=c$ has exactly $6$ solutions?
There are 6 solutions when y = -3 and when y = -4. i.e. a horizontal line at y = -3 cuts the curve in 6 places (similarly for y = -4). Hence c = -3 and c = -4. I'll leave you to add them together!
