MIPS- How to Subtract (already used sub- does not work!) - mips

Question

My code comes up with Unsupported R-Type, how do I make it subtract correctly. Tried changing other details within.... Already tried using subu...............................................................................................
.data
str: .asciiz "\nHello World!\n"
# You can change what is between the quotes if you like
.text
.globl main
main:
# Do the addition
# For this, we first need to put the values
# to add into registers ($t0 and $t1)
li $t0, 30 # You can change the 10
li $t1, 20 # You can change the 20
# Now we can add the values in $t0
# and $t1, putting the result in special register $a0
sub $a0, $t0, $t1
# Set up for printing the value in $a0.
# A 1 in $v0 means we want to print an int
li $v0, 1
# The system call looks at what is in $v0
# and $a0, and knows to print what is in $a0
syscall
# Now we want to print Hello World
# So we load the (address of the) string into $a0
la $a0, str
# And put a 4 in $v0 to mean print a string
li $v0, 4
# And just like before syscall looks at
# $v0 and $a0 and knows to print the string
syscall
# Nicely end the program
li $v0, 0
jr $ra

Answer 1

Your program runs fine in the mars and spim simulators except for program termination. These simulators don't set up $ra, so it's zero. So, at the end, you're returning to something that may have semi-random instructions, including an illegal one. Thus, it's not your sub at all that is the problem. It's what happens later.
Change:
# Nicely end the program
li $v0, 0
jr $ra
Into:
# Nicely end the program
li $v0, 10
syscall