So 1 USD = 0.77 EUD and 1 USD = 1.24 CAD
Which implies that 0.77 EUD = 1.24 CAD, and by dividing both sides by 1.24, we can find out what 1 Canadian dollar is in terms of Euros.
I take it the input of 5 is an input of 5 European dollars (since EUD is the independent variable), so substitute 5 for EUD and find out how many CAD you get...
2. Let S represent the sale price of the computers and P can be the original price (for example).
If the original price is discounted by 15%, then the sale price is 85% of the original price. If a $200 rebate is then added, that means you'd save another $200, so subtract that from the sale price as well.
In maths that gives
Then let P = $2500 to find out the sale price.
3. To graph you could input a range of x values, find the corresponding f(x) values, plot the (x, f(x)) coordinates and join them together. With a bit of analysis though, it's easy to see that is the same graph as the graph, translated down by 4 units.