how would i solve this problem step by step?

Solve by using substitution.

7x - 2y = 4
3x + 5y = 10

7x - 2y = 4
2y = 7x - 4
y = [(7x - 4)/2] ...... (1)

3x + 5y = 10

Substitute (1) for y.
3x + 5[(7x - 4)/2] = 10
3x + (35x - 20)/2 = 10
2[3x + (35x - 20)/2] = 2(10)
6x + 35x - 20 = 20
41x = 20 + 20
x = 40/41

3x + 5y = 10

Substitute 40/41 for x.
3(40/41) + 5y = 10
120/41 + 5y = 10
5y = 410/41 - 120/41
y = (290/41)/5
y = (290/41)(1/5)
y = 58/41

∴ x = 40/41, y = 58/41

solve 1 equation for 1 variable
substitute the first equation into the second to find the other variable
then find the first variable with either equation

7x-2y=4
3x+5y=10

-2y = 4 - 7x
y = 7/2x - 2

3x + 5(7/2x - 2) = 10
3x -35/2x -10 = 10
3x - 17x = 20
-14x = 20
x = -20/14 = -10/7

7(-10/7) -2y = 4
-2y = 14
y = -7

3(-10/7) + 5y = 10
-30/7 + 5y = 10
5y = 70/7 + 30/7 = 100/7
y = 100/35

OOPS!! There's a calculation error somewhere. Your homework assignment is to find the error and solve the equation!!