Call x the number of campers on the low trail and y the number of campers on the high trail.
So we have
x + y ≤ 30
x ≥10
y ≥ 5
This has many solutions....(10, 20) (11, 19) (12, 18) ( 13, 17).....etc.......(24,6) (25, 5)
We can graph this...but there will be many "solution" points that aren't whole numbers - and thus - aren't really a part of the solution set because we can't have "part" of a person !!!
The 'graph' is here........https://www.desmos.com/calculator/mxbludbhfr
Tthe solution set lies along the "hypoteneuse" of the grey triangle in the middle of the graph and consists of the points in which x and y are both whole numbers !!!
l = # of low terrain campers
h = # of high trail campers
$$l + h \le 30.$$
$$l \ge 10.$$
$$h \ge 5.$$
See graph: https://www.desmos.com/calculator/evwqbnqf46 [Inspect the right triangle region].
Note the intersection at (10,20).
So, you could have 10 low terrain campers and 20 high trail campers
OR
15 low terrain campers and 10 high trail campers
OR
other combinations!