K Solve the problem. In 10 hr, Kerrie can travel 9 mi upriver and come back. The rate of the current is 4 mph. Find the rate of her boat in still water. Let x= the rate of her boat in still water in mph. The rate traveling upriver (against the current) is x-4 mph. (Type an expression using x as the variable.) The rate traveling back downriver (with the current) is x+4 mph. (Type an expression using x as the variable.) Complete the table. (Type expressions using x as the variable. Use integers or fractions for any numbers in the expression.) d t Up Down