Use your calculator to determine ( 2 )3 to three significant figures in two ways. (a) Find 2 to four significant figures; then cube this number and round to three significant figures. (b) Find 2 to three significant figures; then cube this number and round to three significant figures. (c) Which answer is more accurate? a b Explain.

The answer is, the streetlight is 18 inches tall.

So the first thing we do is to multiply the top equation by 3. the reason i want to do this is i notice there will be a 6y on both equations and can possibly add/subtract them. so we get 6y = -3x + 27. adding that and the second equation we get 6x = 27-15 which is 12. divide by 6 and we get 2. ∴ x = 2. substituting 2 into the first equation we get 2y = -2 + 9 which is 7. divide by 2 and we get 7/2. ∴ y = 7/2, x = 2.