F = m*a
(Force) = (mass x acceleration)
1) Plug the numbers into the corresponding variables using parentheses:
(225) = m*(2.3)
2) Divide 2.3 on each side so that the variable and the numbers are not separate sides
225/2.3 = m* 2.3/2.3
97.83 = m
3) Rewrite your answer.
The combined mass of Sharon and her skateboard is 97.83 kg.
(Remember that kg or kilograms is the proper SI Unit for mass)\
Hope this helps!!