Triangle STU is congruent to triangle UTX is the missing step. AAS (angle-angle-side) is a method of proving 2 triangles congruent, and using the already proved information, you can find the triangles that are congruent by AAS.
Answer:
AAS(Angle-Angle-Side) postulate states that if two angles and the non-included side one triangle are congruent to two angles and the non-included side of another triangle, then the two triangles are congruent
In triangle RAS and triangle QAT
[Angle]
[Side] [Given]
By Base Angle Theorem states that in an isosceles triangle(i.e, AST), the angles opposite the congruent sides(AS =AT) are congruent.
⇒
[By base ∠'s of isosceles triangle are equal]
By definition of supplementary angles, if two Angles are Supplementary when they add up to 180 degrees.
,
are supplementary and
,
are supplementary.
⇒
and
Two
supplementary to equal 
Since,
then, we get;
[Angle]
then, by AAS postulates,

By CPCT[Corresponding Part of Congruent Triangles are equal]
Hence Proved!
we are given

Here,
y is the number of gallons of water in the pool
x is the number of minutes the truck has been filing the pool
now, we will verify each options
option-A:
When x=1
then y=19.75
so, for 1 minute , number gallons =19.75
so, this is FALSE
option-B:
Since, we have

It is similar to equation of line
y=mx+b
But b=0
It means that it passes through origin
so, this is TRUE
option-C:

we can compare it with
y=mx
where m is the rate
so, we get

while we are given
the water in swimming pool increase about 100 gallons by every 5 minutes
so, we get rate as
gallons per minute
this is close to 19.75
so, they are approximately equal
so, this is TRUE
option-d:
x-value and y-value will show relationship
and ratio will always be constant or equivalent
because it has linear relationship
so, this is TRUE
option-e:
We need to check
(8,150) ..so, x=8 and y=150
we can plug this in our equation
and we get


Since, left side is not equal to right side
so, this can not be point
so, this is FALSE