We will solve this using a system of equations. We are first told that building a is 180 feet shorter than b, so our first equation is b = 180 + a. Next we are told that the addition of a and b is 1490, so our second equation is a + b = 1490. We already have the first equation solved for b, so let's sub that into the second equation in place of b: a + (180 + a) = 1490, and 2a + 180 = 1490. 2a = 1310, so building a is 655 feet tall. b is 180 feet taller, so b = 655 + 180, and b = 835 feet tall.