15 more than 3 times a number is at most 7

Let x = the number

"Fifteen more than" means addition

"Three times a number" is multiplication

"three less than" is subtraction, as is the term difference

Putting it all together, we have

7 - (15 + 3x) = (9 - 5x) - 3

-8 + 3x = 6 - 5x

-8 = 6 - 8x

-14 = - 8x

14/8 = 7/4 = x