help me

[tex]A = (-1+4)\times(-1-2)-10:(-5)\\ A = (3)\times(-3)+2\\ A = -9+2\\ A = -7\\\\ B = \frac{7}{5}+ \frac{7}{5}\times \frac{2}{3}\\\\ B= \frac{7}{5}+ \frac{12}{15}\\\\ B= \frac{21}{15}+ \frac{12}{15}\\\\ B= \frac{33}{15}\\\\ C= \frac{3\times10^2\times4\times10^{-9}}{25\times10^{-3}}\\\\ C = \frac{3\times4\times10^2\times10^{-9}}{25\times10^{-3}}\\\\ C = \frac{12\times10^{-7}}{25\times10^{-3}}\\\\ C = \frac{12}{25}\times 10^{-7-(-3)}\\\\ C = 0,48\times10^{-4}\\\\ C = 4,8\times10^{-5} [/tex]