What's the measure of angle /_A?
I don't know if you can see it well enough but...

∠ A = 50°

Step-by-step explanation:

The angle at the centre COB is twice the angle at the circumference CDB

∠ COB = 2 × 65° = 130°

The angles ACO = ABO = 90° ( angle between radius and tangent )

The sum of the angles in quadrilateral ABOC = 360° thus

∠ A = 360° - (90 + 90 + 130)° = 360° - 310° = 50°

see explanation

step-by-step explanation:

a

(6r + 7) + (13 + 7r) ( remove brackets and collect like terms )

= 6r + 7 + 13 + 7r

= 13r + 20

b

remove brackets and collect like terms

13 - r - 1 + r

= 12 - r

c

remove brackets and collect like terms

= - 8 - r + 2r - 4

= - 12 + r

d

remove brackets and collect like terms

= 7r - - - 6r

[-   - = - - = - ]

= r -