For question b, do you know why you keep it at 1- a and not minus the 1 instead?

Step-by-step explanation &

For 8b, the distance between (2,a) and (5,1) is the square-root of the sum of squares of the difference in x and y directions, namely,

d^2 = ((2-5)^2+(a-1)^2 = 9+a^2-2a+1    (1)

We are given d^2=(sqrt(13)^2)= 13

so by substituting d^2=13, equation (1) becomes

a^2-2a+10=13

a^2-2a-3=0           [simplify]

(a-3)(a+1) = 0          [by factoring]

so a=3 or a=-1

If you have a different approach learned from school, please post what you would have done.  It was not clear in the remark you posted.

Thank you!

2/3x + 7 = 29

step-by-step explanation:

two thirds = 2/3

plus a number = x

at least 29 = 29

there for you should get 2/3x + 7 = 29