A Variable is a symbol for a number we don't know yet. It is usually a letter like x or y.
A number on its own is called a Constant.
A Coefficient is a number used to multiply a variable (4x means 4 times x, so 4 is a coefficient)
I did first one only (roughy) but hope it helps
Answer:
28 students were surveyed about their number of visits to the pool last summer.
Answer: d = ±10
<u>Step-by-step explanation:</u>
169 =
+ 
169 = (12)² + 
169 = 144 + 
25 = 
100 = d²
√100 = √d²
±10 = d