Y = 5.5x is a linear equation (i.e. the highest power of the variables is 1). Therefore, the line will be a straight line with a slope of 5.5
We are usually concerned with one reaction. That is, the production of one specific set of products from a specific set of reactants.
The number of values of c/d would be the number of possible ways that a and b could recombine to form different pairs of products c and d. (You might get different reactions at different temperatures, for example. Or, you might get different pars of ions.)
Usually, the number of values of c/d is one (1). (Of course, if you simply swap what you're calling "c" and "d", then you double that number, whatever it is.)
Answer:
$280 dollars
Step-by-step explanation:
When they were leaving

When they returned home, they brought 196 Euros.

They brought back $280 dollars to the United States.