Is x=3 a solution for the equation: 3x + 7 = 13
Why or why not ?

No.

Step-by-step explanation:

There are two different ways to do this - solve for x in the given equation or substitute the value for x and see if you get a true statement.

3x + 7 = 13 subtract 7 from both sides

3x = 6 divide by 3 on both sides

x = 2

3(3) + 7 = 13

9 + 7 = 13

16 ≠ 13

Therefore, x = 3 is not a solution for 3x + 7 = 13.

Option D - 25

Step-by-step explanation:

Given : A sample of rock is found to contain 100 grams of a parent isotope.

To find : How many grams of the parent isotope will remain after two half-lives.

Solution : A sample of rocks contain parent isotope  = 100 gram

After one half life of the parent isotope i.e. divided by 2

After two half lives of the parent isotope means again divide one-half life by 2

Which means 25 gram of the parent isotope will remain after two half lives.

Therefore, Option D is correct -25