Answer:
30
Step-by-step explanation:
We will call the missing value a, so we can write the expression as:
6(3x + 5) = 15x + a + 3x
Applying the distributive property on the left side we get:
Then, adding like terms in the right side, we get:
Therefore, the expressions are equivalent if a is equal to 30.
So, the answer is 30