x: the number of small cones
y: the number of large cones
a "dozen" means 12.
"Adam needs both small and large cones to set up for a soccer practice" mean that x must not be 0, and y must not be 0.
"there are fewer than 30 cones in the storage room." mean that : x+y<30
"He needs at least a dozen large cones." means that y≥12
so we have:
i) x≠0, y≠0, that is x>0, y>0
ii) x+y<30
iii) y≥12
now let's check all choices we have:
x>0 True by i
y≥12 True by iii
x+y≤30 Not True by ii (x+y is smaller than 30, the sum cannot be 30)
y>12 Not true by iii (y may be = 12)
x≥0 Not true by i, Adam needs small cones to (so we are assuming there are some in the storage room. Though this is open to interpretation)
x+y<30 True