Answer properly or i will report and block you.

162 = 182 + 192 – 2(18)(19)cos(z)

256 = 324 + 361 – (684)cos(z)

256 = 685 – (684)cos(z)

–429 = –(684)cos(z)

to the nearest whole degree, the measure of z is
degrees.

16² = 18² + 19² - 2(18)(19)cos(z)

256 = 324 + 361 - (684)cos(z)

256 = 685 - (684)cos(z)

-429 = -684cos(z)

cos(z) = -429/-684

z = cos⁻¹ (0.627)

z = cos⁻¹ (cos 51)    [ Cos 51 = 0.627 ]

z = 51

In short, Your Answer would be: 51

Hope this helps!