Answer:
The system is:




Step-by-step explanation:
The variables of your equations are:


The constraints, which become inequalities are:
<em><u>1. The total cost cannot be greater than 1,000 gold</u></em>
- Cost of training m number of marines at 50 gold a piece:

- Cost of purchasing u number of research weapon upgrades at 200 gold per upgrade:


- The cost is limited to 1,000 gold that you are given:

That is the first inequality of your system
<em><u>2. The game allows a maximum of three upgrades:</u></em>
- This sets an upper bound for the variable:

- Add the reasonable constraint that the number of upgrades cannot no be negative:

<em><u>3. You know that you need at least ten marines trained to survive </u></em>
- This sets a lower bound for the variable:

And those are all the four inequalities that form your <em>system to describe the number of marines and the number of upgrades you can train/purchae in the game:</em>



