Question 987576
Lets assume a can do 1/A of the job in a day. and B can do 1/B of the job in a day.

You are told
{{{1 = 10*((1/A) + (1/B))}}}
{{{0.1 = (B+A)/AB}}}
{{{0.1AB = B+A}}}

You are also told that A can do the job in X days. B takes X+5 days

{{{1 = (1/A)X}}}
{{{A=X}}}

{{{1 = (1/B)(X+5)}}}
{{{B = X+5}}}

Now plug those values for A and B into the equation above

{{{0.1(X)(X+5) = X + (X+5)}}}
{{{0.1X^2 + 0.5X = 2X + 5}}}
{{{0.1X^2 -1.5X - 5 = 0}}}
*[invoke quadratic "x", 0.1, -1.5, -5 ]

so A take 17.8 days and B takes 22.8 days by themselves