Someone please help!! Balances these redox equations

Cr2O7^2-(aq)+ I-(aq)-> Cr^3+(aq)+ I2(s)

Iwill give extra points to who gets this right

May someone me with these science questions

Ants live on acacia trees in south america. the ants feed on sugars secreted by the trees. the trees provide room for the ants to live. the ants sting any other insect or animal that comes to eat the trees. what type of relationship is this?