I'm going to make a table of all our information:
color(white)(.) Len g t h color(white)(.) | color(white)(.) Ang l e.Length.∣.Angle
w = 12 color(white)(....) | color(white)(.) W = 58
h = 14 color(white)(. ...) | color(white)(.) H = color(green)(?)
x = color(green)(?)color(white)(4) color(white)(....) | X = color(green)(?)
We'll use SinA/a = SinB/b
Sin (58)/12 = Sin H/14
0.071 = SinH/14
0.989 = SinH
H = Sin^-1(0.989)
H = 81.65
Now our table is
w = 12 color(white)(....) | color(white)(.) W = 58
h = 14 color(white)(. ...) | color(white)(.) H = 81.65
x = color(green)(?)color(white)(4) color(white)(....) | X = color(green)(?)
Since we know a triangle has 180 total degree, we can solve for the last angle, X
180 - 81.65 - 58 = 40.35
w = 12 color(white)(....) | color(white)(.) W = 58
h = 14 color(white)(. ...) | color(white)(.) H = 81.65
x = color(green)(?)color(white)(4) color(white)(....) | X = 40.35
Now we can use SinA/a = SinB/b again
Sin58/12 = Sin40.35/x
0.071 = Sin40.35/x
x = Sin(40.35)/0.071
x = 9.16
Now our table is full
w = 12 color(white)(....) | color(white)(.) W = 58
h = 14 color(white)(. ...) | color(white)(.) H = 81.65
x = 9.16 color(white)(.) | X = 40.35