Thanks! For the first one, you need a comma after the call to filter. I think what you want is:
arrange(filter(ToothGrowth, dose == 0.5), len)
For the second one, you can't end a statement with a pipe, because R is expecting more input. It's like asking R to evaluate 1 + . One plus what? It isn't clear to R that your statement is finished. If you get rid of %>% after arrange(len), then you should be good to go.