Question

Danny writes this sentence:

Answer 1

5x-3=12: The equation

Answer 2

Lets first figure out what each of the words mean in symbols.

Three less: - 3 
a number: x (you can use any variable, but the question says to use x)
five times a number: 5x
is 12: = 12

Now we need to put the equation together.

5x - 3 = 12 is the sequence that Danny wrote.