Data Sufficiency

Is the number of seconds required to travel d1 feet at r1 feet per second greater than the number of seconds required to travel d2 feet at r2 feet per second?

1) d1 is 30 greater than d2

2) r1 is 30 greater than r2


-----------------my doubt----

I understand the reasoning provided in the OG but please let me know why the below method is flawed.

R--T--D
r1 t1 d1
r2 t2 d2

question - is t1 > t2?

t1 = d1/r1------(eq. 1)
t2 = d2/r2------(eq. 2)

using statements 1) and 2) together we have.

t1 = (d2 + 30)/(r2 + 30) ----(eq. 3)
t2 = (d1 - 30)/(r1 - 30) ----(eq. 4)

using eq. 2 & eq. 3

t1 > t2
= (d2 + 30)/(r2 + 30) > d2/r2
= r2(d2 + 30) > d2(r2 + 30)
= 30*r2 > 30*d2
= 1 > d2/r2
= 1 > t2 ---- (eq. 5)

now using eq. 1 & eq. 4
t1 > t2
= d1/r1 > (d1 - 30)/(r1 - 30)
= d1(r1 - 30) > r1(d1 - 30)
= - 30*d1 > -30*r1
= d1/r1 > 1
= t1 > 1 ----- ---- (eq. 6)

combining eq. 5 and eq. 6
t1 > 1 > t2
t1 > t2

I'm thinking the above is flawed because I'm using the same equation to derive equation 5 and 6. Please help. thank you in advance.