The answer is 
.
Solution:
Use algebraic identity: 
For example: 
Given expression 
and 
.
To multiply these equations.
Combine like terms together.
Hence the answer is .
Answer: 10
<u>Step-by-step explanation:</u>
varies directly means: 
Step 1: solve for k ⇒ 
Step 2: plug in the given value and k to solve for the missing value: 
42(5) = 21(x)
2(5) = x
10 = x
Answer:
3(c+4)
Step-by-step explanation:
It would usually be 3 x 4, but since there is a variable, it can`t be multiplied (unless you know what the value of the variable is). Thus the expression is 3(c+4).
