Abundance of each isotope = 0.1900 x100 = 0.001900
0.2500 = 0.002500
88.43 = 0.8843
11.13 = 0.1113
Atomic mass of the element = (135.90714 x 0.001900) + (137.90599 x 0.002500) + (139.90543 x 0.8843) + (141.90924 x 0.1113)
= 0.258223566 + 0.344764975 + 123.718371749 + 15.794498412
= 140.1 amu is the atomic mass of the element