工龄

工 = 二 + 丨 : Mnemonic symbol: a steel beam, since 工 looks like the cross section of a steel beam.

Gitta Giraffe (gu) is working a shift in front of the engine ((e)ng1). Her job is to melt dinosaur bones (丨) so that they can be disposed off easily. To melt the bones, she is shorting a huge capacitor (二) with a steel beam (工) which consequently heats up to a bright glow. Using the glowing hot steel beam she can melt the dinosaur bone easily.

龄 = 令 + 齿 : Li Qingzhao (li) wants to enter engine, but in the kitchen ((e)ng2) she has to undergo a check first. An old codger with an imperial name tag (令) is entitled to check her teeth (齿) in order to now Qingzhao's age (龄).