Since there are 28 grams in an ounce, lets replace oz with the number 28, in your equation.
Thus the equation would look like 79(28) = #of grams.
Now just multiply the two numbers and you will have your answer.
The rationale behind this is that 1 oz = 28 g. So in order to convert 79 oz in to grams, you would need to simply multiply 79 and the number of grams in an ounce to find the answer.
If the problem were converse, and you had to convert from grams to ounces, you would simply divide the number of grams specified by the number of grams in an ounce. This equation would appear as follows: #oz = (#g/28g)