Explanation:
simplifying simply means to combine all terms alike (with variable, without variable) by doing all the arithmetic operations while dissolving parentheses and so on.
(1.62x - 3.21) + (-5.4x + 2.37) =
= 1.62x - 3.21 - 5.4x + 2.37 =
= 1.62x - 5.4x - 3.21 + 2.37 =
= -3.78x - 0.84