The sum of two numbers is 21
the second number is six times the first number
work out the two numbers

First you want to put them in equations. Say the first number is x and the second is y. So we know that x + y = 21 so that will be our first equation then we also know that y is 6 times bigger than x so we get 6x = y. Those are our two equations. Now we see that in the second equation y is already isolated and is equal to 6x so we will replace y in the first equation with 6x. Then we get x + 6x = 21 that can be simplified to 7x = 21 next to find the value of x we will isolate it by dividing each side by 7 then we get x= 3. So then we replace it into one of our equations to find the value of y. For example I will place it in the 6x=y equation and we get 6(3)= y. That goes to 18=y so our two numbers are 3 and 18 which check out and make 21