At first, you have to make an equation to represent both of their weights together. A= Aiden's weight. 30+3A+A=210. You want to add like terms so that is comes out to 30+4A=210.
You want to subtract 30 from both sides; 4A=180
Divide 4 on both sides; A=45
Aiden weighs 45 pounds.
You have to multiply 45 by 3 and add 30; 165
165+45=210
Equation: 30+ 3A+A=210; 30+4A=210
Aiden: 45 pounds
Jonathan: 165 pounds