A star is measured to be 18.9 light years from Earth. What is the correct answer in the calculation shown? (consider both significant digits and scientific notation.)

Electron equations of the given changes are as follow,a)                              cu      →      cu⁺²  + 2e⁻b)                              mg⁺²  +  2 e⁻      →      mgc)                              cl⁻    →      cl  +  1e⁻d)                              s  +  2 e⁻    →      s²⁻e)                                o²⁻      →      o  +  2 e⁻f)                              p  +  3 e⁻    →      p³⁻g)                              fe²⁺    →      fe³⁺  + 1 e⁻h)                              s²⁻    →      s⁴⁺  +  6 e⁻

100cm, because 11.0 cm is 3 figures as they've chosen to include the decimal point. if you have a 3 digit number then anything after the second digit will become 0 if it's to 2 significant figures