Im assuming that the commas are decimal points
8.4( y - 17.9) = 4.2
distribute 8.4 inside the parenthesis
8.4y - 150.36
Take 150.36 to the other side
8.4y = 154.56
divide by 8.4 on both sides to isolate y
\(\frac{8.4y}{8.4}\) = \(\frac{154.56}{8.4}\)
8.4 and 8.4 cancels out
y = 18.4
