One significant figure.
You're dealing with multiplication and division, so you should round the answer to the number of significant figures in the least precise measurement.
In other words, your answer cannot be more precise than the least precise measurement you used when calculating the answer.
In this case, you have
#1.9 ->#two sig figs
#color(blue)(2)color(white)(1.) ->#one sig fig
#color(blue)(4)color(white)(1.) ->#one sig fig
So, start by doing the division
#1.9 div color(blue)(2) = 0.95#
This answer should be rounded to one significant figure, but you should keep at least one extra significant figure as a guard digit.
#0.95 xx color(blue)(4) = 3.8#
At this point, you should round the final answer to
#3.8 = 4 ->#rounded to one significant figure
the answer will be
#1.9 div 2 xx 4 = 4#