31% of 40 is 12.4 exactly
The equation for this would be 4x+3=y where x is months and y is your amount of toys after x months.
plug in 4 for x -> 4(4)+3=y
solve -> 16+3=y
y=19
Add 31 to both sides which will give you
9h = 130
4a + 6b = 10
2a - 4b = 12...multiply by -2
----------------
4a + 6b = 10
-4a + 8b = - 24 (result of multiplying by -2)
------------------add
14b = - 14
b = -14/14
b = -1
2a - 4b = 12
2a - 4(-1) = 12
2a + 4 = 12
2a = 12 - 4
2a = 8
a = 8/2
a = 4
so 12a = 12(4) = 48 <==
