Question 872709
This is a uniform rates doing-a-job type proglem.  The sum of the job parts done is the whole job done.


Let x = the time in minutes for B1 alone to solve the problems.  His work rate is 1/x.


{{{highlight_green((1/x)*3+(1/8)6=1)}}}; You can use x to help find the rate for B2, because once x is found from the first shown equation,  it will no longer be unknown, and you will be able to use: B1_and_B2_Combined=B1+B2, and the units used will be jobs per minute.  Reminder is their combined rate is {{{1/8}}} jobs per minute.



USING THAT DESCRIPTION DISCUSSION AND THEN CONTINUE TO FINISH---------------------
LCD, 8x.
{{{24+6x=8x}}}
{{{24=2x}}}
{{{x=12}}} twelve minutes, rate for B1 is {{{highlight(1/12)}}} jobs per minute.


Combined rate is known, and now B1 rate is known, so we can relate the sum of their rates:
{{{1/12+1/b=1/8}}}, using b as the time for B2 to do the job alone.
LCD is 24b.
{{{24b/12+24b/b=24b/8}}}
{{{2b+24=3b}}}
{{{b=24}}} minutes for B2 to do the job alone.
Rate for B2 is {{{highlight(1/24)}}} jobs per minute.