Math problems for elementary school students

Explanation of the steps:
Cat ++ Mouse =8kg=8𝑘𝑔, Dog ++ Mouse =11kg=11𝑘𝑔, Dog ++ Cat =15kg=15𝑘𝑔, ⇒2(⇒2(Cat ++ Mouse ++ Dog)=8+11+15=34)=8+11+15=34, ⇒⇒ Cat ++ Mouse ++ Dog =34:2=17(kg).