Question 1819
Define w to be the number of acres planted with wheat
Define t (i wont use o as that will be confusing) to be the number of acres planted with oats.

We know the total acreage is 180, so mathematically this is w+t=180.

Also, we know that 20 more acres of wheat were planted, ie w=t+20. 

So we have 2 equations, 2 unknowns...we can solve this.

{{{w+t=180}}}
{{{w-t= 20}}}

Adding them together gives {{{2w=200}}}. Therefore w=100acres.

Hence, t was 80acres.

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2. Again define first number = a and second number = b

So we know that 3a=b (eqn1) and also that a+b = 48 (eqn2)

From equation2, b=48-a. We now sub this into eqn1, giving 3a=48-a. Re-arranging gives 4a=48. Hence a=12.

We then can see that b=36

cheers
Jon.