How to slove for 6≤n+15 for n

6 < n + 15

subtract 15 from both sides to get n alone

-9 < n

then flip the sign to make it correct

so:     n > -9

it's equivalent, so we can say that its equal.

let's call the denominator x and the numerador is 18 less then denominator, x - 18.

multiply

2.x = 5.(x - 18)

2x = 5x - 90

90 = 5x - 2x

90 = 3x

x = 90/3

x = 30

so: