A teacher 3

A teacher gives pens and pencils to elementary students at an equal rate in each classroom.

Pencils	Pens
18	72
29	A
35	140
B	168

Determine the missing value for the letter B.

Correct answer:

B =  42

Step-by-step explanation:

$$\begin{gathered} r=72/18=4 \\ r=A/29 \\ A=29\cdot r=29\cdot 4=116 \\ {r}_2=140/35=4 \\ r=168/B \\ B=168/r=168/4=42 \end{gathered}$$

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