Explanation

Supplementary angles add up to 180°, so set up an equation:

(3x + 5) + (9x - 5) = 180°

Combine like terms:

12x = 180°

Divide both sides by 12:

x = 15°

Explanation

Explanation

• Phenolphthalein is a pH indicator that changes color in response to changes in acidity or basicity.
• In an acidic medium, it is colorless, and in a basic medium, it turns pink.

Explanation

The prefix “pre-” means “before”, as seen in words like preview (before viewing) or predict (say before it happens).

It indicates something happening earlier in time or order.

Explanation

In this sentence, "He's" is a contraction of "He has", showing present perfect tense.

"He has written a letter" is the full form.

Explanation

Adding the suffix “er” to a verb (teach) forms a noun meaning "one who performs the action."

So, teacher is a noun.

Explanation

Stigma is the top part of the carpel where pollen lands and germinates.

It is often sticky to help pollen grains adhere.

Explanation

The sentence uses "Did" + base verb, indicating a question in the past simple tense.

It asks about a completed action in the past.

Explanation

The Operating System (OS) is the core component that manages hardware and software resources.

It acts as the bridge between user and hardware, enabling all system functions.

Explanation

A NAND gate gives output 0 only when all inputs are 1; otherwise, it outputs 1.

It is the inverse (NOT) of the AND gate.