Answer:
10
Step-by-step explanation:
We'll note the numbers as 

You can make this into an inequality, using x as the number of uniforms.
100 + 12x < 61 + 15x
39 < 3x
13 < x, so they must buy more than 13 to get a better deal.
The lowest term would be 16.6
Answer:
-1/3 sqrt(21)
Step-by-step explanation:
1/3 sqrt(21) - 2/3 sqrt(3) * sqrt(7)
We know sqrt(a) * sqrt(b) = sqrt(ab)
1/3 sqrt(21) - 2/3 sqrt(21)
Factor out sqrt(21)
sqrt(21) (1/3-2/3)
sqrt(21) (-1/3)
-1/3 sqrt(21)