Question 156074
AT LEAST YOU WERE CLOSE!!!

Let x=amount of time it takes Stan to mow the lawn alone
Then Stan mows at the rate of 1/x lawn per min
Let y=amount of time it takes Hilda to mow the lawn alone
Then Hilda mows at the rate of 1/y lawn per min
Together, Stan and Hilda mows the lawn at the rate of 1/x + 1/y lawn per min and we are basically told that this equals 1/30 lawn per min

So:
1/x+1/y=1/30  multiply each term by 30xy
30y+30x=xy------------------------------------eq1
Now we are also told that Hilda works twice as fast as Stan, so:

y=x/2 or
x=2y-----------------------------------eq2

Substitute x=2y from eq2 into eq1:
30y+30(2y)=(2y)*y simplify
30y+60y=2y^2 or
2y^2=90y  divide each side by 2
y^2=45y  subtract 45y from each side
y^2-45y=0  Quadratic in standard form with c=0 and it can be factored:
y(y-45)=0
y=0----------------------------not a solution
and 
y=45 min----------------amount of time it takes Hilda working alone
From eq2, x=2y; x=2*45=90 min----------------amount of time it takes Stan working alone

CK
1/45 + 1/90=1/30
2/90 + 1/90=1/30
3/90= 1/30
1/30= 1/30

Hope this helps---ptaylor