You have the following algebraic expression:
17.4x+0.8+6x+17.4r+0.8+bx
In order to simplfy the previous expression, you take into account that you only can sum similar terms. In this case you sum terms with variable x and independet coefficients, just as follow:
17.4x+0.8+6x+17.4r+0.8+bx
= ( 17.4x + 6x + bx ) + (0.8 + 0.8) + 17.4r
= 23.4x + bx + 1.6 + 17.4r
The last expression is the simplified expression.