[First one, aka #13] is a
- If a 20-gallon bathtub is draining at a rate of 2.5 gallons, the max will be 20 gallons. Since it is water/etc, you cannot have negative water, so the least amount will be 0. We now have 0 ≤ ? ≤ 20
- What variable do we use? We are talking about gallons, so we will use g (gallons remaining) to get our answer of a, which is 0 ≤ g ≤ 20
[Second one, aka #11] is d
- I made the system
s - 18 = t
12s = 10t + 32
- Because one sport (s) has 18 less than one technology (t), so s - 18 = t. 12 sport (12s) has 32 more than 10 technology (10t) so if you add 32 to technology, you will get sport (12s = 10t + 32 )
Have a nice day!
I hope this is what you are looking for, but if not - comment! I will edit and update my answer accordingly. (ノ^∇^)
- Heather