Explanation:
First, convert pounds to kilogrammes.
13 lbs are about equal to 5.9 kilos.
Then, do oz to g.
7 ounces is about 198.5 grammes.
100 grammes is the same as .1 kg.
Take 5.9 and add .198 for an approximate result of 6.1 kilos.
For a precise result, use an online conversion service.