Question 647860
This is an equation that can be solved by using PEMDAS (order of operations).

Step 1: Distribute the '8' to the parenthesis. 

{{{8(5-n)-19+17n+21}}}
{{{40-8n-19+17n+21}}}

Step 2: Put like terms together to make it easier to solve

{{{40-19+21-8n+17n}}}

Step 3: Combine like terms

{{{42+9n}}}

The most simplified version of the equation is {{{42+9n}}}

You can write the equation like {{{42+9n}}} or {{{9n+42}}}

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You also asked for help on this equation: {{{-9(4f-6f)+(-15f)}}}

Let's begin like we did with the first and distribute the '-9' to the parenthesis.

Step 1: Distribute the '-9' to the parenthesis

{{{-9(4f-6f)+(-15f)}}}
{{{-36f + 54f - 15f}}}

Remember: A negative (-) times a positive (+) = a negative (-)... A negative (-) times a negative (-) = a positive (+)

Step 2: Combine like terms

{{{-36f + 54f - 15f}}}

All of these numbers have the same variable, so the answer will be one single term.

Let's take it one step at a time.

{{{-36f + 54f - 15f}}}

{{{18f - 15f}}}

Step 3: Combine the last like terms to get the answer

{{{18f - 15f}}}

The answer is {{{3f}}}