-2.3x + 4.2x = 15.01 original equation
1.9x = 15.01 combine like terms
1.9x/1.9 = 15.01/1.9 divide both sides by 1.9 to get x alone
x = 7.9 simplify
CHECK YOUR WORK:
plug in the solution to x into the original equation like so:
-2.3(7.9) + 4.2(7.9) = 15.01 original equation w/ substitute for x
-18.17 + 33.18 = 15.01 simplify multiplication
15.01 = 15.01 simplify addition
When you get an answer like this, you know that the solution to x that you found is correct.