In 15 years lisa will be four times as old as she is now how old is she now

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  Lisa is 5

Step-by-step explanation:

When Lisa is 4 times her current age, 3 times her current age will have been added to her current age. That is, 15 years is 3 times her current age, so Lisa is 5.

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If you want an equation:

  a + 15 = 4a

  15 = 3a . . . . . . . . . subtract a

  15/3 = a = 5 . . . . . Lisa's age is 5

look at the picture.

y-intercept for the function on a picture is 4 → point (0, 4).

y-intercept for the function

is for x = 0. substitute:

y-intercept is 8 → point (0, 8).