Mary's age is twice the sum of john's age and 3. the sum of both ages is 21 years. find the age of each one.

m = 2(j + 3)

m + j = 21

m = 21 - j

equating  first and third equations:-

2(j + 3) = 21 - j

2j + j = 21 - 6

3j =  15

j = 5

so m = 21 - 5 = 16

So Johns age  is 5 and Mary's age is  16  answer

sorry, can't i suggest going to algebra.com

step-by-step explanation:

3. parallelogram

step-by-step explanation:

we turn each of our sides into direction vectors

ab=b-a=(3 - 7, 1 - 0) = (-4, 1)

bc=c-b=(1,6)

cd=d-c=(4,-1)

da=a-d=(-1,-6)

we see how the opposite sides have negated direction vectors; this is characteristic of a parallelogram.   we have congruent sides ab=cd and bc=da with unequal lengths because 1^2+6^2 is different from (-4)^2+1^2.   so it's not a square or a rhombus.  

we check the dot product of direction vectors of adjacent sides.   we have

ab dot bc = -4(1) + 1(6) = 2

that's not zero so the sides are not perpendicular.   we've ruled out rectangle.

the direction vectors indicate two pairs of congruent parallel sides, so we choose parallelogram over trapezoid.