17<=3-2x<=21
subtract 3
14<=-2x<=18
divide by 2
7<=-x<=9
now mutiply whole inequality by -1, this will reveres the inequality
-7>=x>=-9
or -9<=x<=-7
so there are mistakes in the line
the corrected lines are
17 less than or equal to 3 - 2x and 3 - 2x less than or equal to 21 (line one)
14 less than or equal to -2x and -2x less than or equal to 18 (line two)
-7 greater than or equal to x and x greater than or equal to -9 (line three)