bagaimana cara jawabnya dan rumusnya #jawab dong please

[tex] \frac{1}{rp} = \frac{1}{25} + \frac{1}{100} \\ \frac{1}{rp} = \frac{5}{100} \\ rp = \frac{100}{5} = 20[/tex]
seri = 70 + 0,5
= 70,5
total = 70,5 + 20
= 90,5 (A)