Final answer:
The infinitive stem of "valer" used in the future and conditional tenses in Spanish is "valdr-". To this stem, appropriate future and conditional endings are added to form the full verb conjugations.
Step-by-step explanation:
The infinitive stem of "valer" in both the future and conditional tenses in Spanish is valdr-. Unlike other verbs, whose stems remain the same across these tenses, "valer" undergoes a change.
The future tense is formed by adding the future tense endings (-é, -ás, -á, -emos, -éis, -án) to this stem, which results in forms like "valdré" (I will be worth) and "valdrán" (they will be worth).
Similarly, in the conditional tense, the same stem is used with conditional endings (-ía, -ías, -ía, -íamos, -íais, -ían), creating forms such as "valdría" (I would be worth) and "valdrían" (they would be worth).
For example, for the future tense, you would add the endings "é, ás, á, emos, án" to the stem, resulting in forms like "valdré, valdrás, valdrá, valdremos, valdrán". Similarly, for the conditional tense, you would add the endings "ía, ías, ía, íamos, ían" to the stem, giving forms like "valdría, valdrías, valdría, valdríamos, valdrían".