a)
The formula for taking away fractions is :
\[\simplify[std]{a / b + {s1} * (c / d) = (ad + {s1} * bc) / bd}\]
and for this exercise we have $\simplify{b={a1}*x+{b}}$, $\simplify{d={a2}*x+{d}}$.
Hence we have:
\[\simplify[std]{{a} / ({a1}*x + {b}) + ({c} / ({a2}*x + {d})) = ({a} * ({a2}*x + {d}) + {c} * ({a1}*x + {b})) / (({a1}*x + {b}) * ({a2}*x + {d})) = ({a*a2 + c*a1} * x + {a * d + c * b}) / (({a1}*x + {b}) * ({a2}*x + {d}))}\]
b)
Note that the first two fractions are the same as in part a). Hence we immediately have:
\[\begin{eqnarray*} \simplify{{a} / ({a1}x + {b}) + ({c} / ({a2}x + {d}))+{c1}/({a3}x+{d1})}&=&\simplify[std]{({cofx} * x + {con})/ (({a1}*x + {b}) * ({a2}*x + {d}))+{c1}/({a3}x+{d1})}\\&=&\simplify[std]{((({cofx}*x+{con})({a3}x+{d1})+{c1}*({a1}*x + {b}) * ({a2}*x + {d})))/(({a1}*x + {b}) * ({a2}*x + {d})*({a3}x+{d1}))}\\&=&\simplify[std]{(({cofx*a3}x^2+{con*a3+d1*cofx}x+{con*d1})+({c1*a1*a2}x^2+{c1*(a1*d+b*a2)}x+{c1*b*d}))/(({a1}*x + {b}) * ({a2}*x + {d})*({a3}x+{d1}))}\\&=&\simplify[std]{({ans1}x^2+{ans2}x+{ans3})/(({a1}*x + {b}) * ({a2}*x + {d})*({a3}x+{d1}))}\end{eqnarray*}\]