HI

cos is positive here so it must be in the first and fourth quadrant .

x+3= 78.46 , 281.54

x= 75.46 , 278.54 (in degrees)

x= 1.317 , 4.861 (in radians)

(b)

again cos is positive (1st and 4th quadrant)

x=0.795 , 5.488 , 7.078 , 11.77 (in radians)

There are 2 extra solutions (red) because the domain goes up to 4 pi , which means another round . So just add 2pi to 0.795 and 5.488 respectively to get them .