Respuesta :

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  [a] x = 175 - 7.5p

For a, we are isolating the x variable to one side of the equation.

        0.4x + 3p = 70

        0.4x = - 3p + 70

        x =  - 7.5p + 175

  [b] x = 115

For b, we are solving for x when p = 8.

        x =  - 7.5p + 175

        x =  - 7.5(8) + 175

        x = 115