fixed production functions

There are two rms. The first firm has the production function:

f(x; y) = min{2x; x + y}. The

second firm has the production function

f(x; y) = x + min{x; y}.

(a) On the graph below, use red ink to sketch a couple of production isoquants for the first firm

at output levels:

y = 10, and y = 40. Use black ink to sketch a couple of production isoquants

for the second firm at output levels:

y = 20, and y = 30.

this gives a graph with lines going virtical paralell to the y axis and downward with a slope of -1 but I dont know what this means, I have found nothing that helps me interpret it.