b) 12 tens +9 units \( = \)

To solve the expression \( 12 \text{ tens} + 9 \text{ units} \), we can break it down step by step. 1. **Convert tens to units**: - Since 1 ten is equal to 10 units, we can convert 12 tens to units: \[ 12 \text{ tens} = 12 \times 10 = 120 \text{ units} \] 2. **Add the units**: - Now, we add the converted units to the 9 units: \[ 120 \text{ units} + 9 \text{ units} = 129 \text{ units} \] Thus, the final result is: \[ 12 \text{ tens} + 9 \text{ units} = 129 \text{ units} \]