there were 135 buttons in a jar Robin put more bottom into the jar there were 175 buttons in the jar how many groups of 10 buttons did she put in the jar

Since there where originally 135 buttons in a jar and Robin  put more buttons into the jar and the total amount of buttons is 175, subtract the final amount of buttons in the jar by the original amount of buttons in the jar to find how many buttons Robin put in the jar.
T(total) = t1(initial 1) + t2(initial 2); where t1 is the original amount of buttons in the jar, t2 is the amount of buttons put in the jar and T is the total amount of buttons in the jar.
Since we are looking for t2, manipulate the equation to solve for t2.
 t2(initial 2)  =T(total) - t1(initial 1)
Substitute the values of t1 and T.
>  t2(initial 2)  =T(total) - t1(initial 1)
>  t2(initial 2)  =175 -135
>  t2(initial 2)  = 40
Robin put 40 buttons into the jar. 
Since the question is how many groups of 10 buttons did Robin put in the jar, divide 40 by 10.
> 40/10
> 4 
Robin put 4 groups of 10 buttons into the jar.