The chart shows data for four heat engines. which lists the engines from most efficient to least efficient? y, x, w, z z, w, x, y z, x, w, y y, w, x, z

efficiency of the heat engine is calculated by the formula

here we know that

= cold temperature

= hot temperature

now we will find the efficiency of all

1) for W

2) for X

3) For Y

4) for Z

So here most efficient engine is Z and least is Y

so we can arrange it as

Z > X > W > Y

so 3rd option is correct here

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form