1) d + 7/d^2 - 49

2)b^2 - 10b + 21/b^2 - 11b + 28

Please help me.

you have to use brackets to establish the correct order of operation.

you probably meant
(d + 7)/(d^2 - 49)

do you not see the difference of squares pattern in the denominator?
(d + 7)/(d^2 - 49)
= (d + 7)/[(d-7)(d+7)]
= 1/(d-7) , where d cannot be ±7

the second ...
(b^2 - 10b + 21)/(b^2 - 11b + 28)
again is quite easy. Both the top and the bottom factor very nicely.
Why don't you try it yourself, and let me know what you got.

hint: both top and bottom have a factor of (b-7)