$$139-35=104$$  Red kangaroo: $$104 \div2 = 52$$  Gray kangaroo: $$52+35=87$$ 
A red kangaroo and a gray kangaroo weigh $$139\textasciitilde\text{kg}$$ altogether. The red kangaroo weighs $$35\textasciitilde\text{kg}$$ less than the gray kangaroo. How much does the gray kangaroo weigh? 
[1] $$104\text{kg}$$ 
[2] $$52\text{kg}$$ 
[3] $$87\text{kg}$$ 
[4] $$96\text{kg}$$ 
[5] $$53\text{kg}$$ 