the function y=5.45 + 1.05(x+7) can be used to determine the cost of in dollars for a prepaid cell phone plan of x minutes. What is the rate if change of the cost, in dollars, with respect to the number of minutes purchased?

Which of these is a disadvantage of hydrogen fuel cells? a. engines that use hydrogen fuel are more efficient than gasoline-powered engines. b. the only emission produced by hydrogen fuel cells is water. c. hydrogen fuel is continually available and useful for heating. d. hydrogen fuel is often purified in a process that emits lots of greenhouse gases.