If Porsha views four glasses of juice as a perfect substitute for…

If Porsha views four glasses of juice as a perfect substitute for one cup of soda and vice versa, what is her marginal rate of substitution between juice and soda?
Part 2 If soda is measured on the horizontal axis, then Porsha’s marginal rate of substitution of juice for soda is
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(Enter your response rounded to the nearest whole number and include a minus sign if necessary.)