Answer:
Step-by-step explanation:
Answer: 
<u>Step-by-step explanation:</u>

NOTE: The sign between 4x and 7 is missing in the question you posted. I assumed it was 4x + 7 in order to solve the equation.
Equation: 50+15x=200
solution: x= 10
it would take him 10 weeks to purchase the bike he wants.
If we were to foil
after experieence
we know
ax²+bx+c=0
and
in form
(ax+b)(cx+d)=0
if we expand it, we get
acx²+bcx+adx+bd=0
or
(ac)x²+(bc+ad)x+(bd)=0
compare to
ax²+bx+c=0
we notice that the middle terms (x terms) are
b=(bc+ad)
so
in form
(2x-1)(1x+5)
b=bc+ad=(-1*1+2*5)=-1+10=9
b=9
or you could just expand it