The missing angle of (3x-5)

To find the missing angles of the triangle we must first make an equation using what we know. A triangles sum is equal to 180 degrees, and a box indicator represents a 90 degree angle. With that we do this,

(7x+5)+(3x-5)+90=180
7x+5+3x-5+90=180
7x+3x+90=180
10x+90=180
10x=180-90
10x=90
10x/10=90/10
x=9

Now we find each individual missing angle,

(3x-5)
3(9)-5
27-5
22 degrees

(7x+5)
7(9)+5
63+5
68 degrees

Check to make sure it equals 180 degrees

22+68+90=180

A=bxh3.2x1.8=5.76 centimeters square