Question:

1. Identify the first term \(a\) and common difference \(d\):
\[ a = 3, \quad d = 8-3 = 5. \]

2. Let the total number of terms be \(n\). The last term given is \(a_n = 253\). Use the nth‑term formula:
\[ a_n = a + (n-1)d \]
\[ 253 = 3 + (n-1)\times5 \]
\[ (n-1)\times5 = 250 \]
\[ n-1 = 50 \]
\[ n = 51. \]
Hence the AP contains 51 terms.

3. "20th term from the last term" means we count the last term as the 1st term from the end. Therefore the required term is the \( (n-20+1)^{\text{th}} \) term:
\[ \text{Position} = 51 - (20-1) = 32. \]

4. Find the 32nd term using the nth‑term formula:
\[ a_{32} = a + (32-1)d \]
\[ a_{32} = 3 + 31\times5 \]
\[ a_{32} = 3 + 155 = 158. \]

5. Hence the 20th term from the last term of the given AP is 158.