Question

write an algebraic expression for three less than seven times x

Answer 1

For this case what should be done is to follow step by step what the statement tells us.
 So, we have
 three less than: -3
 seven times x: 7x
 therefore, the expression will be
 7x-3
 answer
 three less than seven times x: 7x-3

Answer 2

3-7x so this thing said i have to write at least 20 characters