please show me step by step solving this equation?

1)
Let Mark's present age be x, Jane's present age be y.
x = y+3 ... (1)
x+4 = (3/2)(y+4) ... (2)

(2) - (1):
4 = (1/2)y + 3
(1/2)y = 1
y = 2

Sub. (y=2) into (1),
x = 2+3
x = 5

Therefore, Mark is 5 years old now.

2)
Let Lucy's present age be x, Amy's present age be y.
x = 4y ... (1)
x-3 = 13(y-3) ... (2)

(1) - (2):
3 = -9y + 39
-9y = -36
y = 4

Sub. (y=4) into (1),
x = 4(4)
x = 16

Therefore, Lucy is 16 years old now.

If you haven't learned simultaneous equations, I will show you another method to solve these problems.

1)assume mark's age is x and jane's age is y
x=3+y

x+4 = 1.5y
x=1.5y - 4

3+y = 1.5y - 4

7+y=1.5y
0.5y=7
y=14

x = 17

2)Assume lucy's age is x and amy age is y
x=4y

x-3=13y
x=13y+3

13y+3 = 4y

y=4 so x = 16

Lucy is 16

Let mark is X years old, so Jane is (X-3) years old.
then 4 years later mark will be X+4 and Jane will be (X-3+4) =(X+1)
Mark will be 3/2 as old as Jane
so Mark's age = 3/2 Jane's age
= (X+4) = 3/2(X+1) --- multiply both side by 2 gives
= 2X+8 = 3X+3
= X=5 so Mark is 5 years old

2) Let Lucy is Y years old, so Amy is ((1/4)Y).
3 years ago, Lucy is (Y-3) and Amy is ( (1/4)Y-3 )
Lucy was 13 times as old as Amy, so
(Y-3) = 13((1/4)Y-3) ------ expand it
= Y-3 = (13/4)Y - 39 ------ arrange like terms
= 36 = (9/4)Y
= Y = 36*(4/9)
= Y = 16
so Lucy is now 16 years old