Ineed with 6a and don’t understand how to solve for x

In a

let's say the unmentioned angle is Y

so a line is 180° thus Y+145°=180°

we can get y=35°

so a triangle has inside angle sum of 180 and this gives us

X-25°+X+35°=180°

2X=170°

X=85°

for b

we know the inner angles of any four sided figure is 360°

X-35°+2X-75°+X+X=360°

5X=450°

thus X=90°