math questions

1- Write an equation for computing a  tip in a restaurant. Does your equation represent a function? If so, what are your choices for the independent and dependent variables? If not, select none in the appropriate blanks.

Find  where  is a meal price,  is a tip.

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2-Write a formula to express the following sentence as an equation: The sale price is  off the original price. Use  for sale price and  for original price to express  as a function of 

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I need  it asap