5x - 3y = -11....multiply by 2
2x - 6y = -14 ....multiply by -5
------------------
10x - 6y = -22 (result of multiplying by 2)
-10x + 30y = 70 (result of multiplying by -5)
-----------------add
24y = 48
y = 48/24
y = 2 <====
Find the attachment below.
If 6+t ≤13, then t ≤ 7
6 + t ≤ 13
-6 -6
t ≤ 7
When subtracting 6 from positive 6 they cancel out leaving t. Then 13 - 6 = 7.

Step-by-step explanation:
the question is asking for the volume of water in m^3 that will be in the pool when it is completely full.
we find this by multiplying the length times the width times the depth.
this gives us 50m×25m×2.5m= 3125m^3