[tex]a) \: 2.5 + 6.8 \times {3}^{2} = \frac{25}{10} + \frac{68}{10} \times 9 = \frac{93}{10} \times 9 = \frac{837}{10} = 83.7 \\ \\ b) \: 10.5 - (2 + 3.7) \times \frac{1}{8} = \frac{105}{10} - 5.7 \times \frac{1}{8} = \frac{21}{2} - \frac{57}{10} \times \frac{1}{8} = \frac{21}{2} - \frac{57}{80} = \frac{840 - 57}{80} = \frac{783}{80} [/tex]=9.7875
