If cos x = sin(20 + x)° and 0° < x < 90°, the value of x is (what? )°.

       cos(x) = sin(x + 20)
       cos(x) = sin(x)cos(20) + cos(x)sin(20)
       cos(x)                       cos(x)
              1 = tan(x)cos(20) + sin(20)
          cos(20)           cos(20)
    sec(20) = tan(x) + tan(20)
         1.06 ≈ tan(x) + 0.36
       - 0.36               - 0.36
         0.7 = tan(x)
tan⁻¹(0.7) = tan⁻¹[tan(x)]
          35 = x

0 < x < 90
0 < 35 < 90

The shelves will hold 270 books in total

Idon’t know what the answer is i wish i could