Solve this simultaneous equation: 5n+t= 21 n-3t=9

5n+t= 21n-3t=9
n= 9+3t5(9+3t)+t= 2145+15t+t= 2145+16t= 2116t= -24t= -1.5
5n-1.5= 215n= 22.5n= 4.5