Question

7.8+3.5w-1.5 for w = 6.8

Answer 1

This question is so easy.
7.8+(3.5x6.8)-1.5
=7.8+23.8-1.5
=30.1

Answer 2

first multiple 3.5 with w which is 6.8, then collect 7.8 with the result (23.8) and finally substrack 1.5.
to make it easier after multiple write the numbers on end.