I feel stupid. I am starting a lab and am stumbling at the first question. I don't know how to tell from the map the age of the fluvial landscape I...

I feel stupid. I am starting a lab and am stumbling at the first question. I don't know how to tell from the map the age of the fluvial landscape

I can't tell the gradient on this map. http://www.gigapan.com/gigapans/0de35df32e7646092344651ea4030d61

Map of East Brownsville, TX: What stage of fluvial landscape development is shown on this map?