Question 981076
m = number of marines
u = number of upgrades


You need at least 10 marines, so {{{m >= 10}}}


The number of upgrades could be 0 or some positive number {{{u >= 0}}}


But "The game allows a maximum of three upgrades", which further means {{{u <= 3}}}


it costs 50 gold per marine and 200 gold per upgrade so {{{50m+200u}}} is the total cost for m marines and u upgrades. You have a max of 1000 gold which means {{{50m+200u <= 1000}}}


The system of inequalities is


{{{system(m >= 10,u >= 0,u <= 3,50m+200u <= 1000)}}}


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Side Note: The two inequalities {{{u >= 0}}} and {{{u <= 3}}} can be combined into {{{0 <= u <= 3}}}