How do I get my code for addition of two numbers to work in QtSpim?

Question

I'm new to MIPS and I've written a program to add two user-selected numbers but it's not working. It says Instruction references undefined symbol at 0x00400014. Can someone please go through my code and explain what's wrong? Thank you.

.data

msg1: .asciiz "Enter addend 1: "
msg2: .asciiz "Enter addend 2: "
msg3: .asciiz "Sum = "



.text

li $v0, 4
la $a0, msg1
syscall

li $v0, 5
syscall

move $t0, $v0

li $v0, 4
la $a0, msg2
syscall

li $v0, 5
syscall

move $t1, $v0

add $t2, $t0, $t1

li $v0, 4
la $a0, msg3
syscall

li $v0, 1
move $a0, $t2
syscall

li $v0, 10
syscall