I do not understand this

Question

4 USB sticks and 1 compact disk have a total capacity of 9 gigabytes.

5 USB sticks have 9 gigabytes more capacity than 1 compact disk.

Find the capacity of 1 USB stick and the capacity of 1 compact disk.

Enter the correct answers in the boxes.

USB stick:____  GB

Compact disc: ___ GB

Answer 1

The trick is to find the system of equations in order to find your variables. Here's what we know:

4u + d = 9 (4 USBs and 1 disk contain 9 gigs)

5u = d + 9 (5 USBs have as much capacity as 1 disk plus another 9 gigs)

We can solve this through substitution. we can isolate d by subtracting 9 from both sides:

5u - 9 = d + 9 - 9

5u - 9 = d

Now that we have a value for d, we can place that into the other equation:

4u + 5u - 9 = 9

Combine like terms:

9u - 9 = 9

Add 9 to both sides:

9u - 9 + 9 = 9 + 9

9u = 18

Divide by 9:

9u / 9= 18 / 9

u = 2

Now that we know what u is, we use that to find how much d is by placing that in the substitution equation::

5 * 2 - 9 = d

10 - 9 = d

1 = d

check:

4 * 2 = 1 * 1 = 9

8 + 1 = 9

9 = 9

I hope this breakdown helps you. Look at the information given to you so that you can form the needed system of equations.