Final answer:
To combine like terms, add the coefficients of the like terms together and keep the variable the same. In this case, the equivalent expression with the fewest number of terms is 7x.
Step-by-step explanation:
To combine like terms, add the coefficients of the like terms together and keep the variable the same. In this case, 4x + 3x, the coefficients are 4 and 3 and the variable is x. When we add 4 and 3, we get 7. So, the equivalent expression with the fewest number of terms is 7x.