Carla and Rob left a 20 percent tip after having lunch at a restaurant. The amount of the tip was 6$. Carla's lunch cost $15. Write an equation you can use to find x, the cost of Robs lunch.

Rob lunch costs $15 and an equation that can be used to compute it is x = y - 15, where y is the total amount of the bill minus the tip, that is y = 6/0.2

Step-by-step explanation:

In order to solve this question we can attribute a variable to the total amount spent on this lunch, we'll call it "y". The problem states that a 20% tip was given after lunch and that this value was $6. From this information we can calculate the value of "y". We have:

20%*y = 6

(20/100)*y = 6

0.2*y = 6

y = 6/0.2 = $30

Then the problem tells us that Carla's lunch was $15, so we can calculate the value that Rob spent that will be:

x = 30 - 15 = $15

An equation that can be used to find Rob's lunch value is:

x = y - 15

Since we know that y = 6/0.2 we have:

x = 6/0.2 -15 = 30 - 15

x = ±sqrt(10)

step-by-step explanation:

5 - 2x² = -15

subtract 5 from each side

5-5 - 2x² = -15-5

-2x^2   = -20

divide by -2 on each side

-2x^2   /-2= -20/-2

x^2 =10

take the square root on each side

sqrt(x^2 )=±sqrt(10)

x = ±sqrt(10)

check:

5 - 2x² = -15

+sqrt(10)

5 - 2(sqrt(10))² = -15

5 -2(10) = -15

5 -20 = -15

-15 = -15

-sqrt(10)

5 - 2(-sqrt(10))² = -15

5 -2(10) = -15

5 -20 = -15

-15 = -15