The total bill is $9.50 +3.50 = $13.00. The estimated tip is 15% of $10, so Jamal needs to add 15% of $3, or $0.45, to his estimate to leave a tip equal to 15% of the bill.
The tip Jamal has calculated is about 11.5% of the bill. (1.50/13.00 ≈ 0.1154)
The tip Jamal wants to leave is $1.95. (0.15·13.00 = 1.95)
