The illusionist needs at least 4 female volunteers. This means he could use 4 or more; this means x, the number of female volunteers, is greater than or equal to 4:
x ≥ 4
The total of number of volunteers needed is up to 10. This means the illusionist can use 10 or fewer people; this means the total is less than or equal to 10.
The number of female volunteers is x and the number of male volunteers is y; together they create the expression x+y. This gives us
