Answer:
<h2>140 minutes</h2>Step-by-step explanation:
this problem focuses on the combined work rate
both can finish the work under 63 minute
let bobby mow the lawn in x minute
Billy will then mow the lawn in x-25 minutes
Let the completed job = 1 (a mowed lawn)
we can now apply the combined work formula for the two boys as
multiplying through by x(x-25 )we have
open bracket we have
rearranging and collecting like terms we have
we can now use the quadractic formula
a= 1
b= -151
c= 1575
the first answer x= 139.72 approximately 140 minutes mins is correct for Bobby's time
let us check
we can see that the solution approximates to 1