Astandard form of the possible combinations of only nickels and quarters of $3.80

What is the slope of the line shown below?

Hii1977 cleaner shrimp are a species of shrimp that clean parasites from other organisms. fish allow the shrimp to eat the parasites in their mouth. the shrimp get a source of nutrition. the relationship between the shrimp and the fish is this association indicates that for the smaill aneser arecommensal,mutualistic,or parasitic for the begger one the anser are the shrimp and fish benefit each other , the shrimp harm the fish, or the fish do not benetit from the shrimp

What is the axis of symmetry of the function f(x)=-(x+ 9)(x-21)